Mammalian cells offer a good production system for complex biologic products that require proper post-translational processing and folding. These products can be endogenous proteins, recombinant proteins, or recombinant antibodies, which are often needed in large quantities for clinical evaluations and structural studies. Many cell lines are available for production purposes and are derived from various sources, therefore, exhibiting a wide variety of growth and production characteristics. In general, cell types can be divided into two major categories: those that are able to grow in suspension (anchorage-independent) and those that require a physical support for growth (anchorage-dependent). In either case, the products produced can be secreted into the production medium or can be accumulated inside the cells. The properties of the cells and the location of the produced product dictate the method used for growth and production, and consequently the selection of a suitable type of bioreactor. This unit focuses on the methods used to cultivate large amounts of cells for the purpose of obtaining an endogenous or recombinant product.