Cell culture is practiced extensively throughout the world today. The techniques required to allow cells to grow and be maintained outside the body have been developed throughout the 20th century. In the 50 years since the publication of the first human cancer cell line, HeLa (1 ), thousands of cell lines representing most of the spectrum of human cancer have been derived. These have provided tools to study in depth the biochemistry and molecular biology associated with individual cancer types and have helped enormously in our understanding of normal as well as cancer cell physiology. Although some caution is required in interpreting data obtained by studying cells in vitro, it has allowed investigation of a complex disease such as cancer to be simplified to its component parts. The aim of this chapter is to introduce some of the basic concepts involved in the practice of cell culture.