Understanding the genetic bases of phenotypes associated with the earliest stages of divergence will reveal a great deal about species formation. I review a number of model systems, most involving plant-insect interactions, that have already revealed genetic aspects of incipient speciation. It is suggested that progress in understanding the causal forces driving mating signal evolution and incipient speciation will be expedited in model systems where; (1) ecological and evolutionary information is available, (2) different aspects of mating behaviors that function in mate and/or species recognition are known, (3) genetic analysis of single phenotypes is undertaken, (4) analysis of sexual selection and isolation is performed under natural conditions (or in the wild), and (5) comparative data from related species are available to assess phylogenetic trends.