It is probably true to state that the evolution of cultigens within the genus Phaseolus is as well understood as that of any grain legume species. This is because a great diversity of pertinent evidence has come to light from a range of disciplines in addition to the biological, principally from archaeology and chemistry. At the present time Phaseolus beans are widespread in use both as pulses and green vegetables, particularly the common bean P. vulgaris, and there is considerable interest in their improvement emanating from a wide range of interests. They are of very considerable importance as a subsistence crop in Central and South America as well as in parts of Africa. They are also of commercial interest to the canning and frozen food industries in addition to pulse merchants. Quite obviously the requirements of all these markets are very different. There is therefore the broadest possible interest in the range and extent of the germplasm resources existing in the genus, which can be mobilised to meet the enormous range of actual and potential breeding objectives. The incentives for extensive collection, efficient conservation and evaluation are therefore very considerable and there is ample economic justification for investment in these activities.

One of the most remarkable features of the cultigens of this genus is that they combine very similar basic patterns of morphological divergence from ancestral forms with very marked agro-ecological differentiation.