Apoptosis is related to many diseases and induced by a family of cell death receptors and their ligands. Cell death signals are transduced by death domain (DD)-containing adapter molecules and members of the ICE/CED-3 protease family. Caspases-8 (FLICE) and -10 (FLICE2) are two pivotal members in the ICE/CED-3 protease family. FLICE-inhibitory proteins were identified in virus and human and designated v-FLIPs and FLIP, respectively. The human FLIP was also cloned by several labs independently and termed Casper, I-FLICE, FLAME-1, CASH and CLARP. FLIP contains two death effector domains (DEDs) and a caspase-like domain. FLIP interacts with adapter protein FADD and caspase-8 and -10, and potently inhibits apoptosis induced by all known death receptors. Four splice variants of c-FLIPs have been identified and termed α, β, γ, δ, respectively.