Start with a configuration of sleeping frogs on a graph. At time zero, one frog wakes up and begins a random walk. It awakens any sleeping frogs it lands on, which start their own random walks, and so on. I will discuss some phase transitions exhibited by this process on infinite trees. In particular, I will show that on a binary tree, all frogs wake up, while on a 5-ary or higher tree, some frogs remain asleep forever. This is joint work with Chris Hoffman and Matt Junge.