In Batman: Arkham City for the PS3 and Xbox 360, you can play as Catwoman in various points of the story line, and in the Challenge Map as well.
First, you have to have the Catwoman Bundle Pack which is available via download. All retail versions of the game should have come with a code for a free download, however if you purchased the game used you’ll have to buy the pack.
Once the Catwoman Bundle Pack is downloaded and installed, you’ll be able to select Catwoman on the Challenge Map stages, and you’ll be able to play as her during random points in the story line as well. Catwoman has her own set of moves and gadgets as well, and there are certain Riddler puzzles that can only be solved with Catwoman.