General characteristics of apoptosis and mechanisms leading to activation of caspases and endonucleases, the main executors of apoptosis is described. The crucial role in these processes of mitochondria and the proteins released from them procaspase 9, cytochrom c and AIF factor is also shown. Information is also presented about membrane receptors, their ligands as well as various regulatory proteins, those from BCL-2/BAX and IAPs families included. It is pointed out that changes in the level of expression and/or properties of regulatory proteins characterize various tumor cells.