Testicular dysgenesis syndrome is manifested as poor semen quality, undescended testes, hypospadias, or testicular germ cell cancer. The current hypothesis on the pathogenic events leading to testicular dysgenesis involves improper development of somatic nurse cells and consequently delayed germ cell development. Most evidence comes from testicular germ cell cancer, which is the most common cancer in young men. It develops through a preinvasive carcinoma in situ (CIS) stage. Much data indicate that the CIS cell is a neoplastic and pluripotent counterpart of a primordial germ cell (PGC) or gonocyte that has failed to differentiate. During their development both PGC and gonocytes undergo extensive epigenetic modifi cations, including erasure and reestablishment of genome wide DNA methylation and exchange of histone modifi cations. This chapter reviews the current knowledge on the perinatal reprogramming of fetal germ cells and its possible involvement in testicular cancer pathogenesis.