The concept of programmed cell death, or apoptosis, has exploded into a major scientific field of interest for cell biologists, oncologists, and many other biomedical researchers. Apoptosis occurs throughout the lifetime of most multicellular organisms. During development, for example, the selective death of cells is vital to remove tissue between the digits to produce fingers and toes. Apoptosis is also necessary to destroy cells that represent a threat to the integrity of the organism, for example cells infected by a virus. In many cancers the genes regulating apoptosis are defective, producing immortal, continuously proliferating cells. This book discusses the philosophical and technical difficulties in defining the moment of death for a cell, as well as the biological implications and significance of programmed cell death. Recent developments in the genetic control and interacting gene networks associated with apoptosis are presented. The book is written for advanced undergraduate and postgraduate students, and is highly illustrated to aid understanding.