Numerical taxonomic analyses (particularly agglomerative clustering and ordination) were conducted on 55 species of Medicago, using 75 mostly vegetative and fruiting characters. The material studied represents all conservatively accepted species of the genus, as well as 14 "problematical" species of which many are often considered to belong to the genus Trigonella, rather than to Medicago. Although the characters employed are substantially the same as those used by recent monographers who evaluated the genus by traditional subjective procedures, the present numerical examination suggests many relationships not previously appreciated.As a result of the analyses, it was judged appropriate to recognize 12 groupings. These are group 1: M. sativa (alfalfa) and 11 allied species; group 2: M. lupulina and M. secundiflora; group 3: eight problematical species which have troubled taxonomists with respect to whether they should be placed in Medicago or Trigonella; groups 4–8: each made up of a single divergent species, respectively: M. carstiensis, M. radiata, M. orbicularis, M. heyniana, and M. arborea; groups 9–12 four subgroupings of a larger group of 28 annual species. In the main, the composition of the seven polytypic groups is similar to those of taxa accepted by recent monographers, although some realignments of particular species are suggested by the present study. Groups 1 and 2 are much more similar to each other than indicated in recent treatments. Medicago arborea was discovered to be much more dissimilar to all other species examined than thought previously. Medicago hybrida of group 1 was found to be a "master link" between species traditionally placed in Medicago, and many placed in Trigonella (group 3).The 12 groupings in turn fall into three assemblages that could be recognized as subgenera, or even as genera. These are A: groups 1, 2, 9, 10, 11, and 12; B: groups 3–7, inclusive; and C: M. arborea. Further research is suggested before formal categorization is undertaken.