The goal of research in laboratory evaluation of semen has been to ultimately predict the fertility achievable with use of that semen. Historically, problems deterring realization of this goal include pitfalls in experimental approach as well as a lack of basic understanding of biological mechanisms important to the relationship between semen quality and fertility. The relationship between semen quality and fertility has been masked by poor repeatability of many laboratory tests of semen quality, inability to accurately measure fertility and insufficient variation in fertility over which relationships have been studied. Some biological limitations include a lack of understanding of the interaction of semen quality and quantity on fertility, the effect of the female reproductive tract on selective sperm transport and sperm retention and the influence of spermatozoal traits on fertilization of the ovum and sustenance of embryonic development. A case is presented for the use of heterospermic insemination (competitive fertilization) experiments to more clearly identify components of semen quality important to fertility by reducing or eliminating many factors that mask this relationship. Also, areas of future research important to the evaluation of semen quality and fertility are discussed.