Proliferation and death (apoptosis) are the main cellular functions in the maintenance of the homeostasis of the organism. Disturbances in the regulation of these two basic phenomena may results in the continuous and irreversible accumulation of cells in time and space. This process which could become autonomous without any obvious biological "advantage". Both the overproduction of anti-apoptotic factors (e.g. bcl-2) or the failure of pro-apoptotic signals (e.g. p53) can contribute to tumorigenesis. Authors review the different phases of apoptosis with emphasis on the most important decision making elements in cell death, i.e. caspases and mitochondria, as well as on the interactions of the regulatory pathways. The better understanding of these coordinated and interdependent actions may help to achieve improvements in many fields of oncology.