This talk is for programmers who want to understand how the XNA Framework works on Xbox 360, and the implications for writing high-performance code. The talk explains when and why the framework transitions between the Xbox user and supervisor modes, and why should you care. The talk also presents best practices for writing efficient graphics and math code, how to use multiple cores to parallelize your game, and which XNA Framework APIs can be called reentrantly while doing so. Finally, the talk demonstrates what tools are available for investigating performance on Xbox 360, and how Windows tools can help you understand Xbox 360 performance issues. Speaker: Shawn Hargreaves.