Male fertility in mammals depends on the continuous daily production of millions of spermatozoa. The process of spermatogenesis is one of exquisite complexity, requiring 6 to 9 weeks for completion. The process is controlled by an extraordinary interplay of autocrine, paracrine, and endocrine factors. The AG Schlatt is exploring the many developmental and physiological aspects controlling gamete and androgen production by the testis. In recent years the group has a strong focus on the role of testicular stem cells for maintenance of sperm production. In this context, translational aspects of the research programme range from potential treatment options for infertile patients up to the development of hormone based male contraceptive strategies. The Schlatt team creates the core unit of the Institute of reproductive and regenerative biology providing a number of animal models for the evaluation of testis function. Currently the team holds research colonies of axolotl (Ambystoma mexicanum), several strains of mice and two species of non-human primates (Cynomolgus monkey, Macaca fascicularis; Marmoset, Callthrix jacchus) to explore a wide range of developmental and physiological aspects from basic research to pre-clinical applications. The use of human tissue and cells for in vitro studies provides also a large spectrum of clinically relevant experiments.