Isoflavones are natural substances which elicit a number of physiological effects in living organisms. The substances are synthesized in plant tissues as protective agents against biotic stress (i. e. bacterial infection). Isoflavones are also an important dietary constituent in human nutrition. Modern trends in studies of isoflavones in plant materials and foodstuffs and procedures for chemical analyses of isoflavones in human body fluids and plant tissues are discussed in this review. Highly effective extraction and purification techniques, i. e. solid-phase extraction, accelerated-solvent extraction, and Soxhlet extraction, are presented. Latest procedures in chromatographic separation of isoflavones that apply different types of sorbents are described. Immunochemical analysis, electrochemical sensing of isoflavones, and spectrometric and other analytical techniques and their applications are also mentioned. Special attention is paid to the highly selective and sensitive technique of mass spectrometry and its application for identification of isoflavones and their glucosides in plants. Studies of interactions of isoflavones with cell receptors and a number of biologically active substances such as DNA and proteins are described. The review does not intend to give a complete overview of the topics considered but rather to present modern and most recent methods used in studies of isoflavones.