This chapter is mainly focused on the presentation of spermatogenesis in humans. First, we addressed the history of the acquisition of knowledge of spermatogenesis, the characterization of Sertoli and Leydig cells, and of the blood–testis barrier. In the second part, the different phases of the spermatogenesis, the mitotic and the meiotic processes, are presented with references to recent acquisitions of the role of several proteins. Finally, the process of spermiogenesis including the chromatin condensation, the formation of the acrosome, and the flagellum with the axoneme, its accessory structures and the mitochondria are described.