Male infertility is a prime example of a complex disease: mild phenotypes such as oligozoospermia are multifactorial – combinations of genetic variants as well as lifestyle/environmental factors play a role, whereas severe phenotypes such as azoospermia are monogenic and caused by rare, high-impact genomic variation. However, only a minor fraction of monogenic causes and even less of multifactorial origin has been elucidated. We aim to advance diagnostic accuracy, increase the fraction of pathomechanisticallyexplained infertility, and, thereby, improve personalised patient care. Further, epidemiology indicates that infertile men feature an increased risk for comorbidities (e.g.cardiovascular/metabolic diseases and certain cancers). Thus, diagnosis of infertility has implications far beyond its acute treatment.