Increased understanding of the intricacies of the follicular development and selection processes has been critical to the development of many of the new developments in ovarian stimulation in clinical practice. This chapter reviews these clinically related physiological aspects of ovarian stimulation, and discusses the resulting new concepts of ovarian stimulation. Recent studies have indicated that anti-Mullerian hormone (AMH) may be a more reliable and robust predictor of ovarian response during ovarian stimulation. The long ovarian stimulation protocol combining GnRH agonist with exogenous gonadotropin administration has been the most popular treatment regime for the past 20 years. The objectives of ovarian stimulation in assisted reproductive technology (ART) are evolving. A further development which promises to further reduce the burden of ovarian stimulation is the introduction of a long-acting follicle stimulating hormone (FSH) preparation which greatly reduces the number of injections required during an in vitro fertilization (IVF) treatment cycle.