Publisher Summary This chapter discusses interaction of bacteria and their products with tissue culture cells. Two general considerations apply to the use of cultured cells with bacteria— namely, avoiding contamination of cell cultures and using cells at a consistent phase of growth. Occult contamination of cell cultures can cause erratic cell growth and experimental results that cannot be repeated. Overt contamination of cell cultures causes loss of valuable time and occasionally loss of valuable cell lines. The second general consideration, culturing cells to a consistent phase of growth, requires that cells be split and seeded consistently for experiments. Typically, cells are used just before reaching confluence, equivalent to growth covering approximately 80% of the growing surface, to ensure that the cells are in log phase growth. Further, the chapter discusses the use of polarized, differentiated, and multiple layer cell culture systems. Multiple layer cell culture systems attempt to incorporate the complexities of interactions between barrier cells and supporting cells, such as epithelial and endothelial cell bilayer, or endothelial and smooth muscle cell bilayers.