Regulated transforming growth factor-? (TGF?) superfamily signalling is an integral part of normal testicular development and the processes that enable the production of fertile sperm. Through shared utilization of receptors, signal transduction components and inhibitors, many ligands in this family exhibit functional overlaps; this facet of their function is critical to understand because these ligands are often co-expressed and, hence, they may compete with or compensate for one another, depending on the specific cellular context. This review describes particular germ cell maturation steps governed by bone morphogenetic proteins, glial cell line-derived neurotrophic factor and activins, focusing on data predominantly from rodent studies that implicate activin and other family members in modulation of gonocyte and spermatogonial stem cell development. We also review knowledge of the TGF? superfamily signalling components in the human testis, exploring their potential impact on the processes associated with disrupted gonocyte development and an enhanced risk of testicular cancer.