Apoptosis (programmed cell death) is an active process that plays a critical role in multiple biologic processes from embryologic development, to lymphocyte development and selection, and homeostasis. The two major mechanisms of cell death are referred to as the intrinsic and extrinsic pathways. These pathways lead to a cascade of events that ultimately converge to the activation of an effector enzyme, caspase-3. Caspase-3 is a cysteine protease with aspartic specificity and a well-characterized effector of apoptosis or programmed cell death signaling. The pro-form of caspase-3 (p32 caspase-3) is sequestered as a zymogen, where upon proteolysis at a conserved DEVD sequence, is converted to the active (p17 caspase-3) enzyme capable of disassembling the cell. Cell death can become disregulated under various conditions and multiple disease states (e.g., viral infection, carcinogenesis, and metastasis). Sensitive and reproducible detection of active caspase-3 is critical to advance the understanding of cellular functions and multiple pathologies of various etiologies. Here, we provide two simple and reproducible methods to measure active caspase-3 in multiple cell types and conditions using a flow cytometric-based analysis.