Several semen parameters are used to discriminate the fertile male from the subfertile male. The most widely used parameters are sperm concentration, motility, progressive motility, and sperm morphology. Semen analysis is usually applied as described in the World Health Organization manual for semen analysis. In addition to a routine semen analysis, sperm functional tests have been described for many years, which in most cases are regarded as research tools and not part of the routine semen testing in an infertility clinic. In this review we report on the value of four sperm function tests: the sperm penetration assay, the sperm-zona pellucida binding tests, the acrosome reaction, and the hyaluronan binding assay. For each test we describe the current value, the indication for performing the test, how to interpret the results, and its therapeutic implications. Our data show that sperm functional assays are highly predictive of IVF outcome results and have the potential to assist in clinical decision making, especially to avoid the current long-standing treatment with IUI and to direct the patients to intracytoplasmic sperm injection without delay when sperm functional testing fails. We believe that advances in molecular biology techniques will allow us to develop simpler sperm function assays in the near future. This will undoubtedly help clinicians in optimizing male factor infertility diagnosis and treatment.