diff --git a/api/lua/examples/default/default_config.lua b/api/lua/examples/default/default_config.lua
index 252ed5c..f9b6c5e 100644
--- a/api/lua/examples/default/default_config.lua
+++ b/api/lua/examples/default/default_config.lua
@@ -4,6 +4,7 @@ require("pinnacle").setup(function(Pinnacle)
     local Output = Pinnacle.output
     local Tag = Pinnacle.tag
     local Window = Pinnacle.window
+    local Layout = Pinnacle.layout
 
     local key = Input.key
 
@@ -83,35 +84,18 @@ require("pinnacle").setup(function(Pinnacle)
         tags[1]:set_active(true)
     end)
 
-    -- Spawning must happen after you add tags, as Pinnacle currently doesn't render windows without tags.
-    Process.spawn_once(terminal)
+    --------------------
+    -- Layouts        --
+    --------------------
 
-    -- Create a layout cycler to cycle layouts on an output.
-    local layout_cycler = Tag.new_layout_cycler({
-        "master_stack",
-        "dwindle",
-        "spiral",
-        "corner_top_left",
-        "corner_top_right",
-        "corner_bottom_left",
-        "corner_bottom_right",
+    local layout_handler = Layout.new_handler({
+        Layout.builtins.master_stack,
     })
 
-    -- mod_key + space = Cycle forward one layout on the focused output
-    Input.keybind({ mod_key }, key.space, function()
-        local focused_op = Output.get_focused()
-        if focused_op then
-            layout_cycler.next(focused_op)
-        end
-    end)
+    Layout.set_handler(layout_handler)
 
-    -- mod_key + shift + space = Cycle backward one layout on the focused output
-    Input.keybind({ mod_key, "shift" }, key.space, function()
-        local focused_op = Output.get_focused()
-        if focused_op then
-            layout_cycler.prev(focused_op)
-        end
-    end)
+    -- Spawning must happen after you add tags, as Pinnacle currently doesn't render windows without tags.
+    Process.spawn_once(terminal)
 
     for _, tag_name in ipairs(tag_names) do
         -- nil-safety: tags are guaranteed to be on the outputs due to connect_for_all above
diff --git a/api/lua/pinnacle-api-dev-1.rockspec b/api/lua/pinnacle-api-dev-1.rockspec
index ef7d345..01c9a14 100644
--- a/api/lua/pinnacle-api-dev-1.rockspec
+++ b/api/lua/pinnacle-api-dev-1.rockspec
@@ -28,5 +28,6 @@ build = {
         ["pinnacle.window"] = "pinnacle/window.lua",
         ["pinnacle.util"] = "pinnacle/util.lua",
         ["pinnacle.signal"] = "pinnacle/signal.lua",
+        ["pinnacle.layout"] = "pinnacle/layout.lua",
     },
 }
diff --git a/api/lua/pinnacle.lua b/api/lua/pinnacle.lua
index 249bcd4..51e3028 100644
--- a/api/lua/pinnacle.lua
+++ b/api/lua/pinnacle.lua
@@ -19,6 +19,10 @@ local pinnacle = {
     window = require("pinnacle.window"),
     ---@type Process
     process = require("pinnacle.process"),
+    ---@type Util
+    util = require("pinnacle.util"),
+    ---@type Layout
+    layout = require("pinnacle.layout"),
 }
 
 ---Quit Pinnacle.
@@ -44,7 +48,10 @@ function pinnacle.setup(config_fn)
 
     config_fn(pinnacle)
 
-    client.loop:loop()
+    local success, err = pcall(client.loop.loop, client.loop)
+    if not success then
+        print(err)
+    end
 end
 
 return pinnacle
diff --git a/api/lua/pinnacle/grpc/client.lua b/api/lua/pinnacle/grpc/client.lua
index 6142d26..c01d800 100644
--- a/api/lua/pinnacle/grpc/client.lua
+++ b/api/lua/pinnacle/grpc/client.lua
@@ -170,7 +170,7 @@ end
 
 ---@nodoc
 ---@param grpc_request_params GrpcRequestParams
----@param callback fun(response: table)
+---@param callback fun(response: table, stream: H2Stream)
 ---
 ---@return H2Stream
 function client.bidirectional_streaming_request(grpc_request_params, callback)
@@ -209,7 +209,7 @@ function client.bidirectional_streaming_request(grpc_request_params, callback)
                 end
 
                 local response = obj
-                callback(response)
+                callback(response, stream)
 
                 response_body = response_body:sub(msg_len + 1)
             end
diff --git a/api/lua/pinnacle/grpc/protobuf.lua b/api/lua/pinnacle/grpc/protobuf.lua
index 0fdaa38..a6b6bef 100644
--- a/api/lua/pinnacle/grpc/protobuf.lua
+++ b/api/lua/pinnacle/grpc/protobuf.lua
@@ -18,6 +18,7 @@ function protobuf.build_protos()
         PINNACLE_PROTO_DIR .. "/pinnacle/process/" .. version .. "/process.proto",
         PINNACLE_PROTO_DIR .. "/pinnacle/window/" .. version .. "/window.proto",
         PINNACLE_PROTO_DIR .. "/pinnacle/signal/" .. version .. "/signal.proto",
+        PINNACLE_PROTO_DIR .. "/pinnacle/layout/" .. version .. "/layout.proto",
         PINNACLE_PROTO_DIR .. "/google/protobuf/empty.proto",
     }
 
diff --git a/api/lua/pinnacle/layout.lua b/api/lua/pinnacle/layout.lua
new file mode 100644
index 0000000..7068547
--- /dev/null
+++ b/api/lua/pinnacle/layout.lua
@@ -0,0 +1,321 @@
+local client = require("pinnacle.grpc.client")
+local protobuf = require("pinnacle.grpc.protobuf")
+
+---The protobuf absolute path prefix
+local prefix = "pinnacle.layout." .. client.version .. "."
+local service = prefix .. "LayoutService"
+
+---@type table<string, { request_type: string?, response_type: string? }>
+---@enum (key) LayoutServiceMethod
+local rpc_types = {
+    Layout = {
+        response_type = "LayoutResponse",
+    },
+}
+
+---Build GrpcRequestParams
+---@param method LayoutServiceMethod
+---@param data table
+---@return GrpcRequestParams
+local function build_grpc_request_params(method, data)
+    local req_type = rpc_types[method].request_type
+    local resp_type = rpc_types[method].response_type
+
+    ---@type GrpcRequestParams
+    return {
+        service = service,
+        method = method,
+        request_type = req_type and prefix .. req_type or prefix .. method .. "Request",
+        response_type = resp_type and prefix .. resp_type,
+        data = data,
+    }
+end
+
+---@class LayoutArgs
+---@field output OutputHandle
+---@field windows WindowHandle[]
+---@field tags TagHandle[]
+---@field output_width integer
+---@field output_height integer
+
+---@class Builtin
+---@field layout fun(self: self, args: LayoutArgs): { x: integer, y: integer, width: integer, height: integer }[]
+
+---@class Builtin.MasterStack : Builtin
+---Gaps between windows, in pixels.
+---
+---This can be an integer or the table { inner: integer, outer: integer }.
+---If it is an integer, all gaps will be that amount of pixels wide.
+---If it is a table, `outer` denotes the amount of pixels around the
+---edge of the output area that will become a gap, and
+---`inner` denotes the amount of pixels around each window that
+---will become a gap.
+---
+---This means that, for example, `inner = 2` will cause the gap
+---width between windows to be 4; 2 around each window.
+---
+---Defaults to 4.
+---@field gaps integer | { inner: integer, outer: integer }
+---The proportion of the output taken up by the master window(s).
+---
+---This is a float that will be clamped between 0.1 and 0.9
+---similarly to River.
+---
+---Defaults to 0.5.
+---@field master_factor number
+---The side the master window(s) will be on.
+---
+---Defaults to `"left"`.
+---@field master_side "left"|"right"|"top"|"bottom"
+---How many windows the master side will have.
+---
+---Defaults to 1.
+---@field master_count integer
+
+local builtins = {
+    ---@type Builtin.MasterStack
+    master_stack = {
+        gaps = 4,
+        master_factor = 0.5,
+        master_side = "left",
+        master_count = 1,
+    },
+}
+
+---@param args LayoutArgs
+---
+---@return { x: integer, y: integer, width: integer, height: integer }[]
+function builtins.master_stack:layout(args)
+    local win_count = #args.windows
+
+    if win_count == 0 then
+        return {}
+    end
+
+    local width = args.output_width
+    local height = args.output_height
+
+    ---@type { x: integer, y: integer, width: integer, height: integer }[]
+    local geos = {}
+
+    local master_factor = math.max(math.min(self.master_factor, 0.9), 0.1)
+    if win_count <= self.master_count then
+        master_factor = 1
+    end
+
+    local rect = require("pinnacle.util").rectangle.new(0, 0, width, height)
+
+    local master_rect
+    local stack_rect
+
+    if type(self.gaps) == "number" then
+        local gaps = self.gaps --[[@as integer]]
+
+        rect = rect:split_at("horizontal", 0, gaps)
+        rect = rect:split_at("horizontal", height - gaps, gaps)
+        rect = rect:split_at("vertical", 0, gaps)
+        rect = rect:split_at("vertical", width - gaps, gaps)
+
+        if self.master_side == "left" then
+            master_rect, stack_rect = rect:split_at("vertical", math.floor(width * master_factor) - gaps // 2, gaps)
+        elseif self.master_side == "right" then
+            stack_rect, master_rect = rect:split_at("vertical", math.floor(width * master_factor) - gaps // 2, gaps)
+        elseif self.master_side == "top" then
+            master_rect, stack_rect = rect:split_at("horizontal", math.floor(height * master_factor) - gaps // 2, gaps)
+        else
+            stack_rect, master_rect = rect:split_at("horizontal", math.floor(height * master_factor) - gaps // 2, gaps)
+        end
+
+        if not master_rect then
+            assert(stack_rect)
+            master_rect = stack_rect
+            stack_rect = nil
+        end
+
+        local master_slice_count
+        local stack_slice_count = nil
+
+        if win_count > self.master_count then
+            master_slice_count = self.master_count - 1
+            stack_slice_count = win_count - self.master_count - 1
+        else
+            master_slice_count = win_count - 1
+        end
+
+        -- layout the master side
+        if master_slice_count > 0 then
+            local coord
+            local len
+            local axis
+
+            if self.master_side == "left" or self.master_side == "right" then
+                coord = master_rect.y
+                len = master_rect.height
+                axis = "horizontal"
+            else
+                coord = master_rect.x
+                len = master_rect.width
+                axis = "vertical"
+            end
+
+            for i = 1, master_slice_count do
+                local slice_point = coord + math.floor(len * i + 0.5)
+                slice_point = slice_point - gaps // 2
+                local to_push, rest = master_rect:split_at(axis, slice_point, gaps)
+                table.insert(geos, to_push)
+                master_rect = rest
+            end
+        end
+
+        table.insert(geos, master_rect)
+
+        if stack_slice_count then
+            assert(stack_rect)
+
+            if stack_slice_count > 0 then
+                local coord
+                local len
+                local axis
+                if self.master_side == "left" or self.master_side == "right" then
+                    coord = stack_rect.y
+                    len = stack_rect.height / (stack_slice_count + 1)
+                    axis = "horizontal"
+                else
+                    coord = stack_rect.x
+                    len = stack_rect.width / (stack_slice_count + 1)
+                    axis = "vertical"
+                end
+
+                for i = 1, stack_slice_count do
+                    local slice_point = coord + math.floor(len * i + 0.5)
+                    slice_point = slice_point - gaps // 2
+                    local to_push, rest = stack_rect:split_at(axis, slice_point, gaps)
+                    table.insert(geos, to_push)
+                    stack_rect = rest
+                end
+            end
+
+            table.insert(geos, stack_rect)
+        end
+
+        return geos
+    else
+        local origin_x = self.gaps.outer
+        local origin_y = self.gaps.outer
+        width = width - self.gaps.outer * 2
+        height = height - self.gaps.outer * 2
+
+        if win_count == 1 then
+            table.insert(geos, {
+                x = origin_x + self.gaps.inner,
+                y = origin_y + self.gaps.inner,
+                width = width - self.gaps.inner * 2,
+                height = height - self.gaps.inner * 2,
+            })
+            return geos
+        end
+
+        local h = height / win_count
+        local y_s = {}
+        for i = 0, win_count - 1 do
+            table.insert(y_s, math.floor(i * h + 0.5))
+        end
+        local heights = {}
+        for i = 1, win_count - 1 do
+            table.insert(heights, y_s[i + 1] - y_s[i])
+        end
+        table.insert(heights, height - y_s[win_count])
+
+        for i = 1, win_count do
+            table.insert(geos, { x = origin_x, y = origin_y + y_s[i], width = width, height = heights[i] })
+        end
+
+        for i = 1, #geos do
+            geos[i].x = geos[i].x + self.gaps.inner
+            geos[i].y = geos[i].y + self.gaps.inner
+            geos[i].width = geos[i].width - self.gaps.inner * 2
+            geos[i].height = geos[i].height - self.gaps.inner * 2
+        end
+
+        return geos
+    end
+end
+
+---@class Layout
+local layout = {
+    builtins = builtins,
+}
+
+---@param handler LayoutHandler
+function layout.set_handler(handler)
+    client.bidirectional_streaming_request(
+        build_grpc_request_params("Layout", {
+            layout = {},
+        }),
+        function(response, stream)
+            local request_id = response.request_id
+            local index = handler.index
+
+            ---@diagnostic disable-next-line: invisible
+            local output_handle = require("pinnacle.output").handle.new(response.output_name)
+
+            ---@diagnostic disable-next-line: invisible
+            local window_handles = require("pinnacle.window").handle.new_from_table(response.window_ids or {})
+
+            ---@diagnostic disable-next-line: invisible
+            local tag_handles = require("pinnacle.tag").handle.new_from_table(response.tag_ids or {})
+
+            ---@type LayoutArgs
+            local args = {
+                output = output_handle,
+                windows = window_handles,
+                tags = tag_handles,
+                output_width = response.output_width,
+                output_height = response.output_height,
+            }
+
+            local geos = handler.layouts[index]:layout(args)
+
+            local body = protobuf.encode(".pinnacle.layout.v0alpha1.LayoutRequest", {
+                geometries = {
+                    request_id = request_id,
+                    geometries = geos,
+                    output_name = response.output_name,
+                },
+            })
+
+            stream:write_chunk(body, false)
+        end
+    )
+end
+
+---@class LayoutHandlerModule
+local layout_handler = {}
+
+---@class LayoutHandler
+---@field index integer
+---@field layouts { layout: fun(self: self, args: LayoutArgs): { x: integer, y: integer, width: integer, height: integer }[] }[]
+local LayoutHandler = {}
+
+---@param layouts { layout: fun(self: self, args: LayoutArgs): { x: integer, y: integer, width: integer, height: integer }[] }[]
+---@return LayoutHandler
+function layout_handler.new(layouts)
+    ---@type LayoutHandler
+    local self = {
+        index = 1,
+        layouts = layouts,
+    }
+
+    setmetatable(self, { __index = LayoutHandler })
+
+    return self
+end
+
+---@param layouts { layout: fun(self: self, args: LayoutArgs): { x: integer, y: integer, width: integer, height: integer }[] }[]
+---
+---@return LayoutHandler
+function layout.new_handler(layouts)
+    return layout_handler.new(layouts)
+end
+
+return layout
diff --git a/api/lua/pinnacle/tag.lua b/api/lua/pinnacle/tag.lua
index a29b626..bfad68d 100644
--- a/api/lua/pinnacle/tag.lua
+++ b/api/lua/pinnacle/tag.lua
@@ -250,7 +250,7 @@ end
 ---layout_cycler.prev(Output.get_by_name("HDMI-1"))
 ---```
 ---
----@param layouts Layout[]
+---@param layouts LayoutOld[]
 ---
 ---@return LayoutCycler
 function tag.new_layout_cycler(layouts)
@@ -393,7 +393,7 @@ local layout_name_to_code = {
     corner_bottom_left = 6,
     corner_bottom_right = 7,
 }
----@alias Layout
+---@alias LayoutOld
 ---| "master_stack" # One master window on the left with all other windows stacked to the right.
 ---| "dwindle" # Windows split in half towards the bottom right corner.
 ---| "spiral" # Windows split in half in a spiral.
@@ -412,7 +412,7 @@ local layout_name_to_code = {
 ---Tag.get("Tag"):set_layout("dwindle")
 ---```
 ---
----@param layout Layout
+---@param layout LayoutOld
 function TagHandle:set_layout(layout)
     ---@diagnostic disable-next-line: redefined-local
     local layout = layout_name_to_code[layout]
diff --git a/api/lua/pinnacle/util.lua b/api/lua/pinnacle/util.lua
index 661f919..ba4e8eb 100644
--- a/api/lua/pinnacle/util.lua
+++ b/api/lua/pinnacle/util.lua
@@ -77,4 +77,126 @@ function util.batch(requests)
     return responses
 end
 
+-- Geometry stuff
+
+---@class RectangleModule
+local rectangle = {}
+
+---@class Rectangle
+---@field x number The x-position of the top-left corner
+---@field y number The y-position of the top-left corner
+---@field width number The width of the rectangle
+---@field height number The height of the rectangle
+local Rectangle = {}
+
+---Split this rectangle along `axis` at `at`.
+---
+---If `at2` is specified, the split will chop off a section of this
+---rectangle from `at` to `at2`.
+---
+---`at` and `at2` are relative to the space this rectangle is in, not
+---this rectangle's origin.
+---
+---@param axis "horizontal" | "vertical"
+---@param at number
+---@param thickness? number
+---
+---@return Rectangle rect1 The first rectangle.
+---@return Rectangle? rect2 The seoond rectangle, if there is one.
+function Rectangle:split_at(axis, at, thickness)
+    ---@diagnostic disable-next-line: redefined-local
+    local thickness = thickness or 0
+
+    if axis == "horizontal" then
+        -- Split is off to the top, at most chop off to `thickness`
+        if at <= self.y then
+            local diff = at - self.y + thickness
+            if diff > 0 then
+                self.y = self.y + diff
+                self.height = self.height - diff
+            end
+
+            return self
+        -- Split is to the bottom, then do nothing
+        elseif at >= self.y + self.height then
+            return self
+        -- Split only chops bottom off
+        elseif at + thickness >= self.y + self.height then
+            local diff = (self.y + self.height) - at
+            self.height = self.height - diff
+            return self
+        -- Do a split
+        else
+            local x = self.x
+            local top_y = self.y
+            local width = self.width
+            local top_height = at - self.y
+
+            local bot_y = at + thickness
+            local bot_height = self.y + self.height - at - thickness
+
+            local rect1 = rectangle.new(x, top_y, width, top_height)
+            local rect2 = rectangle.new(x, bot_y, width, bot_height)
+
+            return rect1, rect2
+        end
+    elseif axis == "vertical" then
+        -- Split is off to the left, at most chop off to `thickness`
+        if at <= self.x then
+            local diff = at - self.x + thickness
+            if diff > 0 then
+                self.x = self.x + diff
+                self.width = self.width - diff
+            end
+
+            return self
+        -- Split is to the right, then do nothing
+        elseif at >= self.x + self.width then
+            return self
+        -- Split only chops bottom off
+        elseif at + thickness >= self.x + self.width then
+            local diff = (self.x + self.width) - at
+            self.width = self.width - diff
+            return self
+        -- Do a split
+        else
+            local left_x = self.x
+            local y = self.y
+            local left_width = at - self.x
+            local height = self.height
+
+            local right_x = at + thickness
+            local right_width = self.x + self.width - at - thickness
+
+            local rect1 = rectangle.new(left_x, y, left_width, height)
+            local rect2 = rectangle.new(right_x, y, right_width, height)
+
+            return rect1, rect2
+        end
+    end -- TODO: handle error if neither
+
+    os.exit(1)
+end
+
+---@return Rectangle
+function rectangle.new(x, y, width, height)
+    ---@type Rectangle
+    local self = {
+        x = x,
+        y = y,
+        width = width,
+        height = height,
+    }
+    setmetatable(self, { __index = Rectangle })
+    return self
+end
+
+local r = rectangle.new(0, 0, 100, 100)
+local r1, r2 = r:split_at("horizontal", 96, 4)
+
+print(require("inspect")(r1))
+print(require("inspect")(r2))
+
+util.rectangle = rectangle
+
 return util
diff --git a/api/lua/pinnacle/window.lua b/api/lua/pinnacle/window.lua
index 8fae79a..c7c49bb 100644
--- a/api/lua/pinnacle/window.lua
+++ b/api/lua/pinnacle/window.lua
@@ -425,7 +425,7 @@ end
 ---    focused:set_geometry({})                       -- Do nothing useful
 ---end
 ---```
----@param geo { x: integer?, y: integer, width: integer?, height: integer? } The new location and/or size
+---@param geo { x: integer?, y: integer?, width: integer?, height: integer? } The new location and/or size
 function WindowHandle:set_geometry(geo)
     client.unary_request(build_grpc_request_params("SetGeometry", { window_id = self.id, geometry = geo }))
 end
diff --git a/api/protocol/pinnacle/layout/v0alpha1/layout.proto b/api/protocol/pinnacle/layout/v0alpha1/layout.proto
index 393bebd..bf0905f 100644
--- a/api/protocol/pinnacle/layout/v0alpha1/layout.proto
+++ b/api/protocol/pinnacle/layout/v0alpha1/layout.proto
@@ -7,20 +7,22 @@ import "pinnacle/v0alpha1/pinnacle.proto";
 // Love how the response is the request and the request is the response
 
 message LayoutRequest {
-  // Respond to a layout request from the compositor.
+  // A response to a layout request from the compositor.
   message Geometries {
     // The id of the request this layout response is responding to.
     //
     // Responding with a request_id that has already been responded to
     // or that doesn't exist will return an error.
     optional uint32 request_id = 1;
+    // The output this request is responding to.
+    optional string output_name = 2;
     // Target geometries of all windows being laid out.
     //
     // Responding with a different number of geometries than
     // requested windows will return an error.
-    repeated .pinnacle.v0alpha1.Geometry geometries = 2;
+    repeated .pinnacle.v0alpha1.Geometry geometries = 3;
   }
-  // Request a layout explicitly.
+  // An explicit layout request.
   message ExplicitLayout {}
 
   oneof body {
diff --git a/pinnacle-api-defs/build.rs b/pinnacle-api-defs/build.rs
index 62d8aaa..adae15b 100644
--- a/pinnacle-api-defs/build.rs
+++ b/pinnacle-api-defs/build.rs
@@ -14,6 +14,7 @@ fn main() {
         formatcp!("../api/protocol/pinnacle/tag/{VERSION}/tag.proto"),
         formatcp!("../api/protocol/pinnacle/window/{VERSION}/window.proto"),
         formatcp!("../api/protocol/pinnacle/signal/{VERSION}/signal.proto"),
+        formatcp!("../api/protocol/pinnacle/layout/{VERSION}/layout.proto"),
     ];
 
     let descriptor_path = PathBuf::from(std::env::var("OUT_DIR").unwrap()).join("pinnacle.bin");
diff --git a/pinnacle-api-defs/src/lib.rs b/pinnacle-api-defs/src/lib.rs
index a1abc55..30ef083 100644
--- a/pinnacle-api-defs/src/lib.rs
+++ b/pinnacle-api-defs/src/lib.rs
@@ -68,6 +68,12 @@ pub mod pinnacle {
             );
         }
     }
+
+    pub mod layout {
+        pub mod v0alpha1 {
+            tonic::include_proto!("pinnacle.layout.v0alpha1");
+        }
+    }
 }
 
 pub const FILE_DESCRIPTOR_SET: &[u8] = tonic::include_file_descriptor_set!("pinnacle");
diff --git a/src/api.rs b/src/api.rs
index 2fa3895..61dc44c 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -1,3 +1,4 @@
+pub mod layout;
 pub mod signal;
 pub mod window;
 
diff --git a/src/api/layout.rs b/src/api/layout.rs
new file mode 100644
index 0000000..c033d0d
--- /dev/null
+++ b/src/api/layout.rs
@@ -0,0 +1,56 @@
+use pinnacle_api_defs::pinnacle::layout::v0alpha1::{
+    layout_request::{self, ExplicitLayout},
+    layout_service_server, LayoutRequest, LayoutResponse,
+};
+use tonic::{Request, Response, Status, Streaming};
+
+use super::{run_bidirectional_streaming, ResponseStream, StateFnSender};
+
+pub struct LayoutService {
+    sender: StateFnSender,
+}
+
+impl LayoutService {
+    pub fn new(sender: StateFnSender) -> Self {
+        Self { sender }
+    }
+}
+
+#[tonic::async_trait]
+impl layout_service_server::LayoutService for LayoutService {
+    type LayoutStream = ResponseStream<LayoutResponse>;
+
+    async fn layout(
+        &self,
+        request: Request<Streaming<LayoutRequest>>,
+    ) -> Result<Response<Self::LayoutStream>, Status> {
+        let in_stream = request.into_inner();
+
+        run_bidirectional_streaming(
+            self.sender.clone(),
+            in_stream,
+            |state, request| match request {
+                Ok(request) => {
+                    if let Some(body) = request.body {
+                        match body {
+                            layout_request::Body::Geometries(geos) => {
+                                // dbg!(&geos);
+                                if let Err(err) = state.apply_layout(geos) {
+                                    // TODO: send a Status and handle the error client side
+                                    tracing::error!("{err}")
+                                }
+                            }
+                            layout_request::Body::Layout(ExplicitLayout {}) => {
+                                // TODO: state.layout_request(output, windows)
+                            }
+                        }
+                    }
+                }
+                Err(_) => (),
+            },
+            |state, sender, join_handle| {
+                state.layout_state.layout_request_sender = Some(sender);
+            },
+        )
+    }
+}
diff --git a/src/config.rs b/src/config.rs
index 66a17c8..fbb12ae 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,7 +1,7 @@
 use crate::{
     api::{
-        signal::SignalService, window::WindowService, InputService, OutputService, PinnacleService,
-        ProcessService, TagService,
+        layout::LayoutService, signal::SignalService, window::WindowService, InputService,
+        OutputService, PinnacleService, ProcessService, TagService,
     },
     input::ModifierMask,
     output::OutputName,
@@ -17,6 +17,7 @@ use std::{
 use anyhow::Context;
 use pinnacle_api_defs::pinnacle::{
     input::v0alpha1::input_service_server::InputServiceServer,
+    layout::v0alpha1::layout_service_server::LayoutServiceServer,
     output::v0alpha1::output_service_server::OutputServiceServer,
     process::v0alpha1::process_service_server::ProcessServiceServer,
     signal::v0alpha1::signal_service_server::SignalServiceServer,
@@ -477,6 +478,7 @@ impl State {
         let output_service = OutputService::new(grpc_sender.clone());
         let window_service = WindowService::new(grpc_sender.clone());
         let signal_service = SignalService::new(grpc_sender.clone());
+        let layout_service = LayoutService::new(grpc_sender.clone());
 
         let refl_service = tonic_reflection::server::Builder::configure()
             .register_encoded_file_descriptor_set(pinnacle_api_defs::FILE_DESCRIPTOR_SET)
@@ -495,7 +497,8 @@ impl State {
             .add_service(TagServiceServer::new(tag_service))
             .add_service(OutputServiceServer::new(output_service))
             .add_service(WindowServiceServer::new(window_service))
-            .add_service(SignalServiceServer::new(signal_service));
+            .add_service(SignalServiceServer::new(signal_service))
+            .add_service(LayoutServiceServer::new(layout_service));
 
         match self.xdisplay.as_ref() {
             Some(_) => {
diff --git a/src/layout.rs b/src/layout.rs
index 1011798..3ed6d9c 100644
--- a/src/layout.rs
+++ b/src/layout.rs
@@ -1,13 +1,20 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 
+use std::collections::{HashMap, HashSet};
+
+use pinnacle_api_defs::pinnacle::layout::v0alpha1::{layout_request::Geometries, LayoutResponse};
 use smithay::{
     desktop::{layer_map_for_output, WindowSurface},
     output::Output,
     utils::{Logical, Point, Rectangle, Serial, Size},
     wayland::{compositor, shell::xdg::XdgToplevelSurfaceData},
 };
+use tokio::sync::mpsc::UnboundedSender;
+use tonic::Status;
+use tracing::error;
 
 use crate::{
+    output::OutputName,
     state::{State, WithState},
     window::{
         window_state::{FloatingOrTiled, FullscreenOrMaximized},
@@ -34,7 +41,7 @@ impl State {
         }) else {
             // TODO: maybe default to something like 800x800 like in anvil so people still see
             // |     windows open
-            tracing::error!("Failed to get output geometry");
+            error!("Failed to get output geometry");
             return;
         };
 
@@ -49,6 +56,113 @@ impl State {
         }
     }
 
+    pub fn update_windows_with_geometries(
+        &mut self,
+        output: &Output,
+        geometries: Vec<Rectangle<i32, Logical>>,
+    ) {
+        let windows_on_foc_tags = output.with_state(|state| {
+            let focused_tags = state.focused_tags().collect::<Vec<_>>();
+            self.windows
+                .iter()
+                .filter(|win| !win.is_x11_override_redirect())
+                .filter(|win| {
+                    win.with_state(|state| state.tags.iter().any(|tg| focused_tags.contains(&tg)))
+                })
+                .cloned()
+                .collect::<Vec<_>>()
+        });
+
+        let tiled_windows = windows_on_foc_tags
+            .iter()
+            .filter(|win| {
+                win.with_state(|state| {
+                    state.floating_or_tiled.is_tiled() && state.fullscreen_or_maximized.is_neither()
+                })
+            })
+            .cloned();
+
+        let output_geo = self.space.output_geometry(output).expect("no output geo");
+
+        for (win, geo) in tiled_windows.zip(geometries.into_iter().map(|mut geo| {
+            geo.loc += output_geo.loc;
+            geo
+        })) {
+            win.change_geometry(geo);
+        }
+
+        for window in windows_on_foc_tags.iter() {
+            match window.with_state(|state| state.fullscreen_or_maximized) {
+                FullscreenOrMaximized::Fullscreen => {
+                    window.change_geometry(output_geo);
+                }
+                FullscreenOrMaximized::Maximized => {
+                    let map = layer_map_for_output(output);
+                    let geo = if map.layers().next().is_none() {
+                        // INFO: Sometimes the exclusive zone is some weird number that doesn't match the
+                        // |     output res, even when there are no layer surfaces mapped. In this case, we
+                        // |     just return the output geometry.
+                        output_geo
+                    } else {
+                        let zone = map.non_exclusive_zone();
+                        tracing::debug!("non_exclusive_zone is {zone:?}");
+                        Rectangle::from_loc_and_size(output_geo.loc + zone.loc, zone.size)
+                    };
+                    window.change_geometry(geo);
+                }
+                FullscreenOrMaximized::Neither => {
+                    if let FloatingOrTiled::Floating(rect) =
+                        window.with_state(|state| state.floating_or_tiled)
+                    {
+                        window.change_geometry(rect);
+                    }
+                }
+            }
+        }
+
+        let mut pending_wins = Vec::<(WindowElement, Serial)>::new();
+        let mut non_pending_wins = Vec::<(Point<i32, Logical>, WindowElement)>::new();
+
+        for win in windows_on_foc_tags.iter() {
+            if win.with_state(|state| state.target_loc.is_some()) {
+                match win.underlying_surface() {
+                    WindowSurface::Wayland(toplevel) => {
+                        let pending = compositor::with_states(toplevel.wl_surface(), |states| {
+                            states
+                                .data_map
+                                .get::<XdgToplevelSurfaceData>()
+                                .expect("XdgToplevelSurfaceData wasn't in surface's data map")
+                                .lock()
+                                .expect("Failed to lock Mutex<XdgToplevelSurfaceData>")
+                                .has_pending_changes()
+                        });
+
+                        if pending {
+                            pending_wins.push((win.clone(), toplevel.send_configure()))
+                        } else {
+                            let loc = win.with_state_mut(|state| state.target_loc.take());
+                            if let Some(loc) = loc {
+                                non_pending_wins.push((loc, win.clone()));
+                            }
+                        }
+                    }
+                    WindowSurface::X11(_) => {
+                        let loc = win.with_state_mut(|state| state.target_loc.take());
+                        if let Some(loc) = loc {
+                            self.space.map_element(win.clone(), loc, false);
+                        }
+                    }
+                }
+            }
+        }
+
+        for (loc, window) in non_pending_wins {
+            self.space.map_element(window, loc, false);
+        }
+
+        self.fixup_z_layering();
+    }
+
     pub fn update_windows(&mut self, output: &Output) {
         let Some(layout) =
             output.with_state(|state| state.focused_tags().next().map(|tag| tag.layout()))
@@ -78,6 +192,10 @@ impl State {
             .cloned()
             .collect::<Vec<_>>();
 
+        self.layout_request(output.clone(), tiled_windows);
+
+        return;
+
         self.tile_windows(output, tiled_windows, layout);
 
         let output_geo = self.space.output_geometry(output).expect("no output geo");
@@ -468,3 +586,137 @@ impl State {
         }
     }
 }
+
+// New layout system stuff
+
+/// A monotonically increasing identifier for layout requests.
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct LayoutRequestId(pub u32);
+
+#[derive(Debug, Default)]
+pub struct LayoutState {
+    pub layout_request_sender: Option<UnboundedSender<Result<LayoutResponse, Status>>>,
+    id_maps: HashMap<Output, LayoutRequestId>,
+    pending_requests: HashMap<Output, Vec<(LayoutRequestId, Vec<WindowElement>)>>,
+    old_requests: HashMap<Output, HashSet<LayoutRequestId>>,
+}
+
+impl State {
+    pub fn layout_request(&mut self, output: Output, windows: Vec<WindowElement>) {
+        let Some(sender) = self.layout_state.layout_request_sender.as_ref() else {
+            error!("Layout requested but no client has connected to the layout service");
+            return;
+        };
+
+        let Some((output_width, output_height)) = self
+            .space
+            .output_geometry(&output)
+            .map(|geo| (geo.size.w, geo.size.h))
+        else {
+            error!("Called `output_geometry` on an unmapped output");
+            return;
+        };
+
+        let window_ids = windows
+            .iter()
+            .map(|win| win.with_state(|state| state.id.0))
+            .collect::<Vec<_>>();
+
+        let tag_ids =
+            output.with_state(|state| state.focused_tags().map(|tag| tag.id().0).collect());
+
+        let id = self
+            .layout_state
+            .id_maps
+            .entry(output.clone())
+            .or_insert(LayoutRequestId(0));
+
+        self.layout_state
+            .pending_requests
+            .entry(output.clone())
+            .or_default()
+            .push((*id, windows));
+
+        // TODO: error
+        let _ = sender.send(Ok(LayoutResponse {
+            request_id: Some(id.0),
+            output_name: Some(output.name()),
+            window_ids,
+            tag_ids,
+            output_width: Some(output_width as u32),
+            output_height: Some(output_height as u32),
+        }));
+
+        *id = LayoutRequestId(id.0 + 1);
+    }
+
+    pub fn apply_layout(&mut self, geometries: Geometries) -> anyhow::Result<()> {
+        tracing::info!("Applying layout");
+
+        let Geometries {
+            request_id: Some(request_id),
+            output_name: Some(output_name),
+            geometries,
+        } = geometries
+        else {
+            anyhow::bail!("One or more `geometries` fields were None");
+        };
+
+        let request_id = LayoutRequestId(request_id);
+        let Some(output) = OutputName(output_name).output(self) else {
+            anyhow::bail!("Output was invalid");
+        };
+
+        let old_requests = self
+            .layout_state
+            .old_requests
+            .entry(output.clone())
+            .or_default();
+
+        if old_requests.contains(&request_id) {
+            anyhow::bail!("Attempted to layout but the request was already fulfilled");
+        }
+
+        let pending = self
+            .layout_state
+            .pending_requests
+            .entry(output.clone())
+            .or_default();
+
+        let Some(latest) = pending.last().map(|(id, _)| *id) else {
+            anyhow::bail!("Attempted to layout but the request was nonexistent A");
+        };
+
+        if dbg!(latest) == dbg!(request_id) {
+            pending.pop();
+        } else if let Some(pos) = pending
+            .split_last()
+            .and_then(|(_, rest)| rest.iter().position(|(id, _)| id == &request_id))
+        {
+            // Ignore stale requests
+            old_requests.insert(request_id);
+            pending.remove(pos);
+            return Ok(());
+        } else {
+            anyhow::bail!("Attempted to layout but the request was nonexistent B");
+        };
+
+        let geometries = geometries
+            .into_iter()
+            .map(|geo| {
+                Some(Rectangle::<i32, Logical>::from_loc_and_size(
+                    (geo.x?, geo.y?),
+                    (geo.width?, geo.height?),
+                ))
+            })
+            .collect::<Option<Vec<_>>>();
+
+        let Some(geometries) = geometries else {
+            anyhow::bail!("Attempted to layout but one or more dimensions were null");
+        };
+
+        self.update_windows_with_geometries(&output, geometries);
+
+        Ok(())
+    }
+}
diff --git a/src/state.rs b/src/state.rs
index a69e3c9..cb5b5d5 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -2,7 +2,8 @@
 
 use crate::{
     api::signal::SignalState, backend::Backend, config::Config, cursor::Cursor,
-    focus::OutputFocusStack, grab::resize_grab::ResizeSurfaceState, window::WindowElement,
+    focus::OutputFocusStack, grab::resize_grab::ResizeSurfaceState, layout::LayoutState,
+    window::WindowElement,
 };
 use anyhow::Context;
 use smithay::{
@@ -98,6 +99,8 @@ pub struct State {
     pub xdg_base_dirs: BaseDirectories,
 
     pub signal_state: SignalState,
+
+    pub layout_state: LayoutState,
 }
 
 impl State {
@@ -277,6 +280,8 @@ impl State {
                 .context("couldn't create xdg BaseDirectories")?,
 
             signal_state: SignalState::default(),
+
+            layout_state: LayoutState::default(),
         };
 
         Ok(state)