diff --git a/lib/nn.js b/lib/nn.js
index 5cce746..327a4eb 100644
--- a/lib/nn.js
+++ b/lib/nn.js
@@ -17,6 +17,10 @@ let tanh = new ActivationFunction(
   y => 1-(y*y)
 );
 
+let ReLU = new ActivationFunction(
+  x => Math.max(0, x),
+  y => Math.sign(y)
+);
 
 class NeuralNetwork {
   constructor(input_nodes, hidden_nodes, output_nodes) {