This review examined current controlled ovarian hyperstimulation (COH) protocols used in ART. Controversies still exist regarding selection of gonadotropin preparation (i.e., recombinant versus urinary forms, pure FSH versus FSH-LH containing preparations), choice of adjuvant therapy with GnRH analogues (agonists versus antagonists), and pretreatment with oral contraceptive pills. Patients prospectively identified as intermediate responders have excellent outcomes with adjuvant therapy with either a GnRH agonist (long protocol) or a GnRH antagonist, but tailoring of gonadotropin dose and type must be performed to achieve optimized results. High responders perform satisfactorily with gentler gonadotropin stimulation regimens that minimize the occurrence of ovarian hyperstimulation syndrome. On the other hand, results in low/poor responders remain sub optimal both in terms of ovarian response and oocyte/embryo quality in spite of a variety of stimulation approaches and adjuvant therapies implemented. It is concluded that ovarian stimulation is a critical step in IVF therapy. There are a variety of available and efficacious novel COH regimens but individualization of management is essential and dependent upon proper and prospective assessment of the ovarian reserve. The identification of the pathogeneses underlying poor ovarian response constitutes a formidable challenge facing reproductive endocrinologists.