The experimental evidence that cultivated plants and their wild relatives regularly exchange genes through pollen transfer under natural conditions is well documented in the literature.However, there has been no consensus regarding long-term ecological or evolutionary consequences of gene flow from cultivated plants into populations of their wild relatives. We review what is known regarding gene flow from crop sorghum, Sorghum bicolor, into populations of its feral congeners, particularly johnsongrass, S. halepense. Descriptions are given of studies conducted on crossability, spontaneous hybridization and fitness of hybrids. The data presented support the hypothesis that crop sorghum commonly contributes alleles to wild/weedy sorghums under field conditions. We focus on the possible consequences of continued gene flow from the crop to wild populations and point out future research needs in this crop/wild complex.