The utility of a focused ion beam (FIB) to provide material removal for micromachining via sputtering with resolution of better than 10 nm has led to many important applications. In addition, FIB combined with a gas source containing the chemical precursors for deposition of materials or for enhanced, selective material removal provides the capabilities for a much wider range of micromachining applications. This chapter introduces FIB material deposition and chemically enhanced material removal processes, lists some of the FIB chemical precursors in common use and discusses the parameters for their use, and presents several examples.