The ovulation method of natural family planning is described in detail as taught in the ovulation method centers with an account of its development in Australia and the underlying philosophy. Hormonal studies supporting its scientific bases are given including recent work on the hormonal events of the menstrual cycle. The teaching of the method for the avoidance and achievement of pregnancy is outlined including special circumstances such as lactation premenopause stress situations abnormal vaginal discharges and formal oral contraceptive use. The failure rate of the ovulation method has been shown by a number of surveys as between that of the pill and the IUD. It is the fastest spreading method of natural family planning currently in use in 50 countries.