Is defined as the cellular events in testis which lead to the formation of male gametes, SPERMS. Occurs in the testis which is a part of male reproductive organs. Spermatogenesis represents the entire process of germ cell development within the seminiferous epithelium of the adult testis.
Occurs in the testis which is a part of male reproductive organs

It can be divided into four phases and includes:
1. The proliferation and differentiation of spermatogonia
2. Meiotic divisions of spermatocytes
3. The transformation of haploid round spermatids arising from the second meiotic division into spermatozoa (spermiogenesis)
4. Release into the lumen of the seminiferous tubules (spermiation)

Spermatogenesis requires lower than normal body temperature as compared to the Oogenesis. This is one of the reasons for testis to descend and become extra-abdominal. The stem cells appear as early as 4thto 5thweeks of IUL in undifferentiated gonads and multiply to form spermatogonia.

The process ceases in IUL itself, again starts around puberty. The child is born with spermatogonia in testis. In the seminiferous tubule, at any given level, the spermatogenic cells are at different stages of differentiation. In each seminiferous tubule, at any given time, the epithelium is at different stages of spermatogenesis. 

This cycle, the spermatogenic cycle, is completed in 22.5 to 23 days. One cycle is not sufficient for completion of spermatogenesis. Instead, it takes 2.5 to 3 cycles; means 72 to 75 days for the spermatogonia to form sperms. While Oogenesis occurs in structural isolation, all the cells in spermatogenesis are interconnected and form a syncytium.