How to construct a simple 2x2 game tree. This is a short clip designed simply to introduce you to the idea of a game tree as a descriptive device for structuring your thinking in strategic interaction. It's almost as simple a situation as we can get: 2 players, each with 2 moves. At this stage don't worry about the "story" behind this game (which can be used to rationalize the preference payoff numbers) - just focus on the logic of constructing the tree. There will be many variations on a simple two player story that might provide "other" trees - ie similar looking 2x2 trees with other patterns of payoffs. In the next clip we take this basic game and analyze it using "rollback reasoning", or "backward induction".