This paper deals with the diversity and biogeography of Trifolium in the Mediterranean Region. Data on 104 species, including 37 Mediterranean endemics and two established aliens, were gathered for 13 south European territories of seven countries: Portugal, Spain, France, Italy, Croatia, Albania and Greece. Species richness, frequency, endemism rate, chorological traits and ecological preferences were studied. The study area encompasses 85% of the Mediterranean Trifolium with 82% of the Mediterranean endemics (sensu Med‐Checklist), most of them restricted to a few localities. Among the rarest species, mainly Mediterranean endemics, seven occur only in one phytogeographical region of Greece (T. andricum, T. argutum, T. caudatum, T. dolopium, T. mesogitanum, T. michaelis, T. phitosianum) and one in Sicily, T. bivonae. The unique Mediterranean endemic reported exclusively for the Iberian Peninsula is T. gemellum, also occurring in Algeria and Morocco. Only 17% of the species occur in all the examined territories: T. campestre, T. repens, T. arvense and T. fragiferum are the most widespread. Multivariate analysis emphasized the connection among the territories with respect to the main centre of diversity and the main geographical east–west gradient of species richness. Greece is the richest country in south Europe with 89 wild species and 30 Mediterranean endemics, whereas Portugal has the lowest number of species (45) and only 6.7% of endemics. Over 60% of the species belong to Mediterranean s.l. chorotypes and 75% are therophytes, living mainly in grasslands, agricultural and ruderal habitats. Trifolium richness is consistent with species–area patterns known for each territory. Some species are still insufficiently studied and additional taxonomical and distributive analyses would be of great interest.