Flops are naturally occurring objects in the minimal model program. Unfortunately, it is difficult to show that they exist. However, Bridgeland discovered that for smooth threefolds, the flop of a map f:Y->X can be constructed as a moduli space of certain perverse sheaves, called perverse point sheaves. These are perverse sheaves which are numerically equivalent to the structure sheaves of points in Y.
We will review flops briefly, then define perverse sheaves and perverse point sheaves. As time permits, we will discuss the proof of Bridgeland's result.