The cysteinyl aspartate-specific proteases (caspases) have been identified as 
key players in the cellular process termed programmed cell death or apoptosis. 
During apoptosis, activated apoptotic caspases cleave selected target proteins 
to execute cell death. Additionally to their established function in cell death, 
a variety of recent publications have provided increasing evidence that 
apoptotic caspases also participate in several non-apoptotic cellular processes. 
Activated caspases exhibit functions during T-cell proliferation and cell cycle 
regulation, but are also involved in the differentiation of a diverse array of 
cell types. In some cell types, their differentiation can be morphologically 
viewed as a kind of incomplete apoptosis. Analysis of well-known apoptotic 
targets of caspases implicates that the cleavage of a limited number of selected 
substrates plays a major role during non-apoptotic functions of caspases. 
Selective substrate cleavage might be regulated by activation of anti-apoptotic 
factors, via a compartmentalized activation of caspases, or through limited 
activity of caspases during apoptosis-independent functions. The increasing 
evidence for caspase function in non-apoptotic cellular events suggests that 
caspases play a much more diverse role than previously assumed.