Adult Leydig cells (ALCs) are specialized cells involved in the production of androgens. They develop during puberty from a stem Leydig cell (SLC) population. These SLCs can be found in the interstitial space of the testis, either centrally located or adjacent to peritubular myoid cells or vessel system. The exact origin of SLCs is still being researched, with most researchers suggesting that they come from mesenchymal cells derived from the mesonephros. However, other sources like the neural crest and coelomic epithelium have also been considered. It is known that luteinizing hormone (LH) plays a crucial role in stimulating Leydig cell development and steroidogenesis. However, the process by which SLCs acquire the ability to respond to stimulations of LH or growth factors is not fully understood. Sertoli cells, which are nearby supportive cells in the testis, or other cell types including peritubular myoid cells, immune cells, and germ cells, release growth factors that may sequentially or collaboratively stimulate the transition from SLCs to later stage Leydig cells before they become sensitive to LH stimulation. Additionally, androgens secreted by fetal Leydig cells may be necessary for the initial development of ALCs. LH signaling is required to further increase the number of Leydig cells and promote the differentiation of later stage intermediates. During puberty in adult rats, approximately 25 million Leydig cells are produced in the testis, and they are responsible for testosterone production.