MLRISC Writing native code generators for modern processors is a significant investment. Unfortunately it is difficult to reuse this investment for other architectures, and even more difficult to reuse for other source language compilers. MLRISC is a customizable optimizing back-end written in Standard ML and has been successfully retargeted to multiple architectures. MLRISC deals elegantly with the special requirements imposed by the execution model of different high-level, typed languages, by allowing many components of the system to be customized to fit the source language semantics and runtime system requirements.