Cell death is a major endpoint in toxicologic assessment both in vivo and in vitro and numerous methods have become available for the characterization and quantitation of cell death. Recent developments in cell biology have made great strides in articulating two generally distinct modes of cell death. Although the Cell Death Nomenclature Committee of the Society of Toxicologic Pathologists has recommended replacing the terms “apoptosis” and “necrosis” with “apoptotic necrosis” and “oncotic necrosis,” emphasizing that necrosis simply refers to the fact that the cells are dead (1), in this chapter we will utilize the more generally used terms apoptosis and necrosis. This chapter will focus on the relative advantages and inherent disadvantages of a number of flow and image cytometry assays with an eye to helping investigators to choose among the many available techniques to measure apoptosis.