In contrast to conventional assisted reproduction techniques in which metaphase II oocytes are retrieved for fertilization in vitro, during the in-vitro maturation of oocytes, immature germinal vesicle stage oocytes are retrieved and matured in the laboratory before fertilization and embryo transfer. Whereas in-vitro maturation is technically more demanding than in-vitro fertilization it carries many potential advantages in terms of lower treatment costs and greater safety, as a result of reducing both the number of clinical consultations and the amount of pharmacological intervention. Although the technology is still experimental, in-vitro maturation has been successfully used for the treatment of patients with polycystic ovarian syndrome, and a number of pregnancies and live births have been reported. Despite these successes and much continuing research effort, the overall efficiency of in-vitro maturation remains low, and neither clinical nor laboratory procedures can be considered to be as robust and routinely feasible as conventional in-vitro fertilization techniques. The immediate goals for in-vitro maturation programmes are therefore to increase germinal vesicle oocyte recovery rates, optimize culture conditions, improve oocyte maturation potential, and after fertilization to produce pregnancy rates that are at least equivalent to those obtained using conventional in-vitro fertilization. This review focuses on the physiology and application of human oocyte maturation in vitro, and will detail the recent advances reported in this rapidly advancing field.