Apoptosis--a programmed cell death--is a general biological mechanism responsible for maintenance of a permanent cell number. Impairment of apoptosis regulation entails disorders in homeostasis and various diseases. This explains biological and medical importance of apoptosis. Molecular grounds of apoptosis regulation, physiological regulation depending on the cell type, examples of apoptosis disregulation leading to definite diseases, approaches to treatment of some diseases basing on knowledge of apoptosis regulation are provided.