diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7d9ae41..286a092 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ Breaking changes:
 
 New features:
 - Added `imul` (#18)
+- Added the golden ratio `phi` (#29)
 
 Bugfixes:
 
diff --git a/src/Math.js b/src/Math.js
index b8a35e9..7c904c2 100644
--- a/src/Math.js
+++ b/src/Math.js
@@ -98,6 +98,8 @@ exports.pi = Math.PI;
 
 exports.tau = 2 * Math.PI;
 
+exports.phi = (1 + Math.sqrt(5)) / 2;
+
 exports.sqrt1_2 = Math.SQRT1_2;
 
 exports.sqrt2 = Math.SQRT2;
diff --git a/src/Math.purs b/src/Math.purs
index 00b36f3..19c8781 100644
--- a/src/Math.purs
+++ b/src/Math.purs
@@ -93,6 +93,10 @@ foreign import pi :: Number
 -- | The ratio of the circumference of a circle to its radius, around 6.283185.
 foreign import tau :: Number
 
+-- | The golden ratio, *φ*, around 1.61803. Two quantities `a` and `b` are said
+-- | to be in the *golden ratio φ* if `(a + b) / a = a / b = φ`.
+foreign import phi :: Number
+
 -- | The Square root of one half, around 0.707107.
 foreign import sqrt1_2 :: Number