The last few years have witnessed an explosion of both interest and knowledge about apoptosis, the process by which a cell actively commits suicide. The number of publications on the topic has increased from nothing in the early 1980s to more than 10,000 papers annually today. It is now well recognized that apoptosis is essential in many aspects of normal development and is required for maintaining tissue homeostasis. The idea that life requires death seems somewhat paradoxical, but cell suicide is essential for an animal to survive. For example, without selective destruction of "non-self" T...