Vitex L. (Lamiaceae, Viticoideae) is taxonomically very complex comprising c. 250 pan-tropical, subtropical and a few temperate species. The most extensive taxonomic revision of the genus was by Pieper for African and Malagasy taxa and goes back to 1928. The need for a modern revision of the whole genus became critical with its recent transference from the Verbenaceae to the Lamiaceae (subfamily Viticoideae). Vitex is a large genus (3.6% of the Lamiaceae s.l.) and its taxonomic position is not of minor taxonomic/evolutionary importance. Vitex is a very important genus in traditional medicine throughout the tropics and especially in Africa. The scientific validation of its traditional medicinal uses requires a solid taxonomy. This book, therefore, provides the first molecular phylogeny reconstruction of the genus and provides explanation about the biogeographical patterns and dating of the molecular phylogeny. Also, an alpha-taxonomic revision of the grex Pilosae is provided based on morphological, molecular and chemical characters. The traditional uses in African medicine of some species were also validated by proving the bioactivities of the essential oils.