The content and composition of essential oils in leaves of Mentha × piperita L., M. spicata L., M. arvensis L., and M. longifolia (L.) Huds. from Estonia were investigated using hydrodistillation and GC-MS analyses. Some chemosystematic markers for the identification of Mentha species are presented. The essential oil yield of the studied species was 2.4-3.0%, 0.9-2.3%, 0.9-1.4%, and 0.7-2.5%, respectively. From the isolated essential oils, 75, 89, 67, and 69 compounds were identified and quantitatively evaluated, representing 92.2-99.5% of the total oil. The main constituents of M. × piperita oils were menthol (26.4-47.7%) and menthone (13.6-31.9%); the ratio of their content was usually between 1 and 3. Four chemotypes of M. spicata were determined: rich in carvone (62.1-67.4%), rich in piperitenone oxide (61.9%), rich in α-terpinyl acetate + trans-β-caryophyllene (61.9% and 11.4%, respectively), and rich in acetic acid,1-methyl-1-(4-methyl-5-oxo-cyclohex-3-enyl) ethyl ether (6.5%). The last two chemotypes were determined for the first time. Only the essential oils of M. arvensis were found to contain trans-1-octen-3-ol (3.8-7.7%) and neryl propionate (2.4% in both samples). Good chemosystematic markers for M. arvensis were also trans-(16.0-19.1%) and cis-β-ocimene (16.0-20.5%). The ocimene-rich chemotype was found by us for the first time. The chemosystematics of M. longifolia was found to be the most complicated, as many chemotypes have been determined by us and several other authors. In this study, a high concentration of carvone (51.4-57.6%) was characteristic of all analysed M. longifolia samples.