Semen analysis is the first step to identify male factor infertility. Standardized methods of semen analysis are available allowing accurate assessment of sperm quality and comparison among laboratories. Population-based reference ranges are available for standard semen and sperm parameters. Sperm numbers and morphology are associated with time to natural pregnancy, whereas sperm motility may be less predictive. Routine semen analysis does not measure the fertilizing potential of spermatozoa and the complex changes that occur in the female reproductive tract before fertilization. Whether assisted reproduction technology (ART) is required depends not only on male factors but female fecundity. Newer tests should predict the success of fertilization in vitro and the outcome of the progeny.