diff --git a/Key-Functions.md b/Key-Functions.md
index 9c63f673b..9b2729cd0 100644
--- a/Key-Functions.md
+++ b/Key-Functions.md
@@ -18,6 +18,8 @@ Instead of using `FNx` when defining `ACTION_*` functions, you can use `F(x)` -
 
 `TO(layer)` - Goes to a layer. This code is special, because it lets you go either up or down the stack -- just goes directly to the layer you want. So while other codes only let you go _up_ the stack (from layer 0 to layer 3, for example), `TO(2)` is going to get you to layer 2, no matter where you activate it from -- even if you're currently on layer 5. This gets activated on keydown (as soon as the key is pressed).
 
+`TT(layer)` - Layer Tap-Toggle. If you hold the key down, the layer becomes active, and then deactivates when you let go. And if you tap it, the layer simply becomes active (toggles on).
+
 
 ### Fun with modifier keys