Apoptosis is currently one of the fastest moving fields in biology with spec- tacular progress made over the past few years in delineating the molecular mechanisms which underlie this process. It is nowindisputable thatapoptosis plays an essential role in normal cell physiology and that aberrant apoptosis can manifest itself in a variety of human disorders. Published in two parts (Volumes 23 and 24 of the series entitled Results and Problems in Cell Dif- ferentiation), this is an attempt to bring together many different aspects of apoptosis. Given that this is such a vast and rapidly...