Spermatogenesis is a complex series of cellular changes leading to the formation of haploid male gametes (spermatozoa) and includes mitotic, meiotic and post-meiotic phases. Spermatogonial stem cells (SSCs) are essential for the continuous lifelong production of spermatozoa. Spermatogenesis is initiated when SSC is triggered to undergo mitosis that gives rise to progenitors, which further differentiate into spermatogonia. In this review, we describe the origin of SSCs and other spermatogonia populations and summarize the knowledge concerning their markers.