Oogenesis is the process of formation of oocyte involving the process of folliculogenesis. Oogenesis begins before birth and the ovaries before birth consist of many primary oocytes. At birth these oocytes are surrounded by follicular cells and this is primary follicle. These remain in the ovary till puberty. As puberty is attained one oocyte completes its cycle. At the beginning primary oocyte is within primary follicle. Oocyte begins its Meiosis I and arrests at Prophase-I. Primary follicle then develops into secondary and further into tertiary follicle but the follicle remains in the arrested prophase-I phase. When tertiary follicle is formed the primary oocyte finally completes its meiosis I and forms secondary oocyte and first polar body after which the tertiary follicle forms the Graffian follicle.