This chapter gives a concise overview of the main mechanisms leading to the specification of primordial germ cells. The molecules and factors involved in the differentiation of the common progenitors of the male and the female gametes of the developing embryo are described. The process involved in the differentiation and maturation of the female gamete and the epigenetic regulations of such events are also discussed. The general features of meiotic division and the specificity of meiosis versus mitosis are evaluated. Fertilization and oocyte activation are compared and the distinct outcomes examined.