The review is dedicated to immunologic adjuvants--various natural and synthetics substances that are added to vaccines for stimulation of specific immune response, but they do not induce specific response themselves. Critically important is the selection of the correct adjuvants, for which mechanisms of effect on immune system are studied the most. The majority of these mechanisms as well as physical-chemical and biological features of modern adjuvants are analyzed in the review. The problem of safety of adjuvants, types of immune response induced by adjuvants of various nature, excipients that are being verified or already in use in modern medicine and veterinary are also examined.