The guide outlines the essence and main directions of the epidemiological approach to the study of human diseases. Particular attention is paid to the specifics of epidemiological studies of infectious and non-infectious pathology, as well as the assessment of the effectiveness and safety of therapeutic, preventive means and measures, diagnostic and screening studies. The method of work with sources of evidence, databases, information systems is reflected, the principles of systematic reviews and meta-analysis are presented . Each of the thematic sections contains modern information sources, existing regulatory and instructional materials . Training questions are worked out when solving situational problems. The annexes contain extracts from the National Standard of the Russian Federation for Clinical Research, the Helsinki Declaration of the World Medical Association, from the informed consent of patients in clinical trials and medical practice, the topic of abstract and scientific-practical works. Designed for students, interns, residents and postgraduates of medical universities, as well as general practitioners .