Infertility affects about 10% of all couples and is defined by a failure to achieve a clinical pregnancy within a year of regular unprotected sexual intercourse. Up to one third of these couples will not have an identifiable cause after routine investigation, id est idiopathic infertility. The current diagnosis of male infertility relies on the World Health Organization (WHO) 2010 criteria which focus on concentration, motility and morphology in comparison to cut-off values of a fertile population. Alas, the relevance of the conventional semen analysis for the choice of treatment and the predictive value for an infertile couple with idiopathic or mild male infertility embarking on medically assisted reproduction (MAR) remains questionable. In other words, there is a strong clinical need to distinguish fertile from infertile men through new sperm function testing and to be able to select both the patient population who will benefit from MAR as well as the type of treatment.