Studies over the last few decades have documented that LH is the principal regulator of Leydig cell function. Recent studies indicate that locally produced intratesticular factors are equally important in modulating Leydig cell development and function. In the present review, results of studies on Leydig development and function with rodent models, in conjunction with recent advances in our understanding, are discussed. Studies on Leydig cell development revealed that there are two different waves of proliferation: the first one is independent of LH and the other is dependent on LH. In addition to LH, FSH plays a major role in Leydig cell development and function by modulating the production of Sertoli cell-derived factors. Studies directed towards understanding the oestrogen-mediated inhibition of Leydig cell proliferation revealed that collagen IV-mediated signalling is involved in Leydig cell proliferation and 17beta-oestradiol inhibits this event. Leydig cell proliferation and differentiation is associated with changes in gene expression. Research in this area has identified several genes that are involved in Leydig cell proliferation and differentiation; the possible role of these genes in the context of Leydig cell development are discussed in this review.