Couples who use contraceptives not only protect themselves against unwanted pregnancies, but also may reduce their risk of becoming infected with a sexually transmitted disease (STD). No currently available method, however, is highly effective in protecting simultaneously against pregnancy and infection. Thus, couples who place high priority on minimizing both risks may have to use two methods. The need for contraceptive methods that provide effective protection against both pregnancy and STDs has been intensified by the HIV epidemic, but progress has been slowed by the lack of integration between the STD and family planning fields. The first part of this two-part article discusses the similarities and differences between the two fields, examines the impact of STDs on contraceptive use and services, and reviews the scientific literature dealing with the effects of condoms, spermicides and barrier-and-spermicide methods on the risk of STD transmission. Part II (which will appear in the next issue) examines what is known about the effects of oral contraceptives, the IUD, tubal sterilization and abortion on reproductive tract infections. The second part also includes a discussion of the trade-offs involved in choosing a contraceptive and presents estimates of the first-year rates of unplanned pregnancy and gonorrhea infection (given an infected partner) that would occur among women using various contraceptive methods.