Ovulation induction, indicated in anovulatory women, is nowadays a major treatment in any cause of infertility. Ovulation induction can be designed to obtained one or two follicles or to obtain a controlled ovarian hyperstimulation. Mild stimulations are used for anovulatory patients or patient with dysovulation, or for intrauterine insemination. Controlled ovarian hyperstimulation aimed at obtaining high number of follicle in In Vitro Fertilization procedure. All ovulation induction should be strictly monitored to prevent complication and mainly multiple pregnancies and the ovarian hyperstimulation syndrome. All ovulation induction should take place after a careful work up of the couple to determine the cause of infertility. This allows to select the best treatment and to avoid complications.