diff --git a/build/math.js b/build/math.js
index 59a3ea6..671be6f 100644
--- a/build/math.js
+++ b/build/math.js
@@ -3674,6 +3674,10 @@ function sinc( x ) {
 
 }
 
+function haversine( x ) { return div( sub( 1, cos(x) ), 2 ); }
+
+function inverseHaversine( x ) { return arccos( sub( 1, mul(2,x) ) ); }
+
 
 // analyticphysics.com / The Complex Gudermannian Function
 
diff --git a/docs/functions.html b/docs/functions.html
index 8f08553..89ac23c 100644
--- a/docs/functions.html
+++ b/docs/functions.html
@@ -70,6 +70,10 @@ <h1>Circular Functions</h1>
 
 <p><a href="functions/sinc.html"><b>sinc( <i>x</i> )</b></a> &mdash; cardinal sine of a real or complex number</p>
 
+<p><b>haversine( <i>x</i> )</b> &mdash; haversine of a real or complex number</p>
+
+<p><b>inverseHaversine( <i>x</i> )</b> &mdash; inverse haversine of a real or complex number</p>
+
 <br id="hyperbolic"/>
 <h1>Hyperbolic Functions</h1>
 
diff --git a/src/functions/trigonometry.js b/src/functions/trigonometry.js
index 29ea8d1..4cb04a8 100644
--- a/src/functions/trigonometry.js
+++ b/src/functions/trigonometry.js
@@ -359,6 +359,10 @@ function sinc( x ) {
 
 }
 
+function haversine( x ) { return div( sub( 1, cos(x) ), 2 ); }
+
+function inverseHaversine( x ) { return arccos( sub( 1, mul(2,x) ) ); }
+
 
 // analyticphysics.com / The Complex Gudermannian Function