In the present paper some aids to the identification of the mints are given. This identification is very complicated indeed, because the species show a great variability, and because hybridization frequently occurs in the genus. In a survey some important, general features of the hybrids are given, e.g. the way in which they differ from the species: their reduced fertility, the occurrence of dwarf pollen and degeneration of the ♂ and ♀ haploid fase, their “hybrid vigour” (heterosis), their variability (which is still much greater than that of the species), and in this connection the “compound segregation” of the seed. Secondly the paper contains a key for the identification of the Dutch species and hybrids, which key may also be useful for a larger part of Europe. In a third survey the main characters of the species and their hybrids are recounted, to check the identification. Of those mints which are very rare or perhaps extinct in Holland, some localities are mentioned.