diff --git a/strings/hamming_distance.rb b/strings/hamming_distance.rb
new file mode 100644
index 0000000..faa738e
--- /dev/null
+++ b/strings/hamming_distance.rb
@@ -0,0 +1,23 @@
+# https://en.wikipedia.org/wiki/Hamming_distance
+
+def hamming_distance(str1, str2)
+  abort 'Strings must be of the same length' unless str1.length == str2.length
+
+  str1.chars.zip(str2.chars).sum { |chr1, chr2| chr1 == chr2 ? 0 : 1 }
+end
+
+if $0 == __FILE__
+  # Valid inputs
+  puts hamming_distance 'ruby', 'rust'
+  # => 2
+  puts hamming_distance 'karolin', 'kathrin'
+  # => 3
+  puts hamming_distance 'kathrin', 'kerstin'
+  # => 4
+  puts hamming_distance '0000', '1111'
+  # => 4
+
+  # Invalid inputs
+  puts hamming_distance 'ruby', 'foobar'
+  # => Strings must be of the same length
+end