Caspases (cysteinyl aspartate-specific proteinases) are cysteine proteases that have a near absolute substrate requirement for aspartate in the P1 position of the peptide bond. Fourteen caspase genes have been identified in mammals [153]. Some caspases (e.g., caspase-12) in human and mouse function differently and have different contributions to cell death mechanisms. Caspases exist as constitutively expressed inactive pro-enzymes (30–50 kDa) in healthy cells. Caspase zymogens are found in different proportions at different subcellular locations. In HeLa cells, most caspase-3 pro-enzyme is found in the cytoplasm, while only 10% is found in mitochondria [154]. In rat heart and brain, 90% of caspase-9 pro-enzyme is mitochondrial [155]. The zymogens contain 3 domains: an amino-terminal pro-domain; a large subunit (~20 kDa); and a small subunit (~10 kDa). Caspases are activated through regulated proteolysis of pro-enzyme with “initiator” caspases activating “executioner” caspases (Table 1; Figure 1). Other caspase family members function in inflammation by processing cytokines (Table 1) [153].