The efficiency of contraceptive techniques is discussed in relation to the motivation of users. Comparative studies of contraceptive effici ency show side variations of efficiency for any particular method, dosage, or device. In addition, it has been found that: most contraceptive failures occur during the early years of a marriage; and have to do with the spacing rather than with the number of children, couples who want few children tend to use more efficient methods from the beginning of the marriage; and contraceptive efficiency tends to improve dramatically once the desired family size has been reached. These findings suggest that the intensity of the couple's motivation may be a crucial factor in contraceptive efficiency; the relational skills of the prescribing physician may be another. The example of contraceptive efficiency in the People's Republic of China is adduced.