Tannins are an extensive group of secondary metabolites widely used in medical practice and in human activities. They are characterized by a wide range of pharmacological activities, including antitumor, astringent, hemostatic, antioxidant and prooxidant, antimicrobial, antiviral, and others. The methods used for the chemical analysis of this group of compounds and for the standardization of tannin-containing types of plant materials have been improved with the development of analytical methods. Addressing the issues of standardization and application of hydrolysable and condensed tannins remain relevant today. This review reflects the main milestones in the historical development of tannin analysis: from using qualitative droplet reactions and physical properties, using the simplest physico-chemical analysis methods to establishing the structure of NMR spectroscopy, and from titrimetric methods using chemical and physico-chemical indicators to modern high-performance chromatography with various types of detectors, as well as the use of combinations of modern physicochemical methods of analysis with mathematical methods for assessing and predicting the qualitative and quantitative composition of tannins and their pharmacological effect. The main types of biological activity of hydrolysable and condensed tannins obtained from plant objects and their mechanisms of action are described.