The textbook describes the most common laboratory and instrumental diagnostic methods in clinical practice, including clinical and biochemical blood tests, studies of the hemostasis system, immunological studies, electrocardiography, ultrasound, radiological, radionuclide and endoscopic research methods, methods for modern assessment of the functional state of internal organs and systems. The technique of each method, indications and contraindications to its use, methods for assessing deviations from normal indicators and interpreting the results obtained are described in detail.