The mammalian oocyte is formed early in foetal life and may remain suspended at diplotene of the first meiotic prophase until several decades later. When, following follicular recruitment, the oocyte enters a growth phase where it increases in volume, and undergoes replication and redistribution of the cytoplasmic organelles. These modifications, including secretion of the zona pellucida, reflect a period of intensive RNA synthesis as the oocyte grows and accumulates the molecular program for embryogenesis. Throughout oocyte development follicle cell support is fundamental to provide the germ line cell with nutrients and growth regulators to ensure progression through the protracted growth phase. Conversely, the oocyte actively promotes growth and differentiation of the follicular cells. Finally, re-initiation of meiosis in mature oocytes results in the production of haploid gametes which are capable of supporting early embryo development. Our present knowledge of the molecular biology of mammalian oogenesis is discussed in this review.