This chapter describes the practical details involved in the successful sectioning of plastic-embedded specimens for electron microscopy. The focus will be on those parts of the process that are really key to the successful sectioning of any biological material, i.e., the proper shape and size of the specimen, sharp knives and how to make them, and the orientation of specimen and production of ultrathin sections onto water-filled boats attached to either glass or diamond knives. This chapter is designed to assist the beginner in microtomy in understanding more fully the terms and basic principles involved in producing ultrathin sections of most plastic-embedded biological specimens.