This review of the literature is focused on the functions and the mechanisms of action of the antimicrobial peptides known to occur in the oral cavity. These compounds make up the first line of the protection of the tissues of the oral cavity against the intrusion of pathogenic agents. A few groups of antimicrobial peptides of different origin exhibiting the antibacterial, antifungal, and antiviral activities have been found in the oral cavity. In addition, some of them possess the properties of immunomodulators and chemoattractants. The antimicrobial peptides play the most important role in maintaining the healthy oral cavity. It has been shown that their production is correlated with the development of periodontitis and multiple dental caries. The possibilities of the practical application of antimicrobial peptides for diagnostics and treatment of the pathological changes in the oral cavity are discussed.