Learned mate preferences may play an important role in speciation. Sexual imprinting is a process whereby mate preferences are affected by learning at a very young age, usually using a parent as the model. We suggest that while the origins of learning appear to lie in the advantages of individual recognition, sexual imprinting results from selection for recognition of conspecifics. This is because efficient early learning about one's own species is favoured in the presence of heterospecifics. If different species are hybridizing, both sexual imprinting and learning to avoid heterospecifics during adulthood promote assortative mating and hence speciation. As a result of sexual imprinting, speciation may also be completed in allopatry when divergence between populations is sufficient to prevent interbreeding when the populations reunite, even in the absence of genetic evolution of mate preference. The role of behaviour and learning in completing the speciation process is relatively overlooked. In particular the evolution of sexual imprinting as a result of selection against hybridization warrants more study.