The female reproductive cycle is based on a co-ordinated function of several regulatory elements and signalling systems. Of the approximately 7 million oocytes present in the human fetal ovary, only 475 will eventually ovulate. In the human, the development of a primordial follicle into a dominant one takes about 10 weeks. Approximately 300 follicles are recruited initially for growth and development, 30 of them are likely to become gonadotropin-dependent and enter competition for dominance and, finally, only one will achieve ovulation. The mechanisms by which follicle stimulating hormone, luteinizing hormone, growth factors and steroids may promote or disrupt follicular development are discussed in detail. Possible implications of these new facts on diagnosis and treatment of ovulatory disturbances are described.