This chapter reviews current understanding of the control of spontaneous preovulatory follicular development in the natural ovarian cycle as a basis for the design and use of superovulation strategy before clinical IVF. The principles, limitations and practical aims of therapy using clomiphene citrate and HMG to stimulate multiple follicular development are outlined together with details of methods in current use to monitor ovarian response to these drugs and to time ovulation induction and egg collection with HCG. Examples of successful IVF treatment cycles are given. It is stressed that properly controlled clinical trials to judge the relative merits of the various superovulation methods in current use for IVF have not been undertaken. Possible new approaches to ovarian stimulation before IVF include the use of 'pure' FSH, LHRH and pulsatile gonadotrophin administration.