Apoptosis is a distinctive form of cell death that reflects cleavage of a subset of intracellular polypeptides by proteases known as caspases. Two major intracellular caspase cascades, one activated predominantly by death receptor ligands and the other triggered by various cellular stresses, including DNA damage and microtubule disruption, have been delineated. Activation of these protease cascades is tightly regulated by a number of polypeptides, including Bcl-2 family members, inhibitor of apoptosis proteins, and several protein kinases. The demonstration that many antineoplastic agents induce apoptosis in susceptible cells raises the possibility that factors affecting caspase activation and activity might be important determinants of anticancer drug sensitivity. Here, we review recent studies describing the regulation of apoptotic pathways and identify potential implications of these findings for resistance to antineoplastic agents.