The main functions of the male reproductive system are the synthesis and secretion of male sex steroids (androgens), production of male gametes (spermatozoa), and transport of sperm into the female genital tract. The development, maturation, and normal function of male fertility are mainly under the control of the hypothalamic-pituitary-testicular axis, which constitutes the hormonal component of an interplaying and intercommunicating neuronal and endocrine system, that will be explained in this chapter.

In this review we reflect on the many attempts highlighting key achievements in the field of in vitro spermatogenesis made so far. The research in this field is at a crucial juncture. The evolving technologies (like biofabricated 3D organoids, 3D bioprinting, microfluidics, or organ-on-a-chip) may offer excellent tools and in vitro testicular model systems to advance our understanding and bridge the existing knowledge gaps. Each of these culture systems offers unique advantages and may complement each other to address the common goal of achieving primate spermatogenesis in vitro. There are various possibilities and future scenarios for applying in vitro spermatogenesis as a tool for research and clinical applications in the future.