The article is devoted to an analysis of the significance of bacteriophages’ discovery in the subsequent development of medicine: from the prevention and control of infectious bacterial diseases to the study of global evolutionary mechanisms by genetic engineering methods. French researcher Felix d’Hérelle discovered bacteriophages when he found a “substance” that kills dysentery bacteria in 1917. A virus by nature, it was called a “bacteria devourer” (bacteriophage). Long before the discovery of antibiotics, d’Hérelle found that bacteriophages were a universal specific antibacterial agent that was safe for humans. In Russia, interest in the study of bacteriophages arose in the early 1920s. In 1939, the renowned Soviet microbiologist Z.V. Ermolieva created a cholera bacteriophage preparation. During World War II in besieged Stalingrad, she produced the cholera bacteriophage in huge volumes and prevented an epidemic of cholera in the Red Army – an important factor in the victory in the Battle of Stalingrad. New molecular biology and genetics technologies have made it possible to reveal the underlying interaction processes of a bacteriophage with a bacterial cell: lysogeny (inclusion of a moderate bacteriophage into the genome of a bacterial cell) and the phenomenon of lysogenic conversion (Eugene and Elizabeth Wollman, 1936), genetic recombination – the mutual exchange of genes between two different lines of bacteriophages (M. Delbruck, S. Luria, A. Hershey, 1946, 1952), integrated with the cell’s DNA, the asymptomatic presence of the virus (pro-bacteriophage), and its activation by the inductive effect of ultraviolet radiation, radiation and a number of chemical factors (A. Lwoff, 1965). Nowadays, the study of molecular genetic mechanisms of embedding, regulation, repression, and induction of bacteriophage activity within a bacterium is important for understanding the mechanisms of heredity, tissue growth and development mechanisms of some forms of tumors. © Andrey V. Ermolaev, Tatiana S. Sorokina.