Three crossability groups have been identified in the wild progenitor of lentil, Lens culinaris ssp. orientalis. The common one which is predominant in this taxon and in the cultigen, the unique one, which at present is known only from three populations in southern Turkey and northern Syria and the intermediate one, known from four populations in that general region. Crosses between members of the common and unique groups yield aborted seeds which can be rescued by embryo culture. Members of the intermediate group are cross-compatible with both other groups. Crossability potential seems to be controlled by a few major genes and minor genes of quantitative nature. One population of the unique group is characterized by novel karyotype and chromosome rearrangements and is reproductively isolated from any other population of Lens culinaris. The implication of the three crossability groups and the novel chromosome rearrangement for lentil taxonomy are briefly discussed.