"Oh, stewardess?"

Safe sex is sexual activity engaged in by people who have taken precautions to protect themselves against sexually transmitted infections (STIs) such as HIV/AIDS. It is also referred to as safer sex or protected sex, while unsafe or unprotected sex is sexual activity engaged in without precautions. Some sources prefer the term safer sex to more precisely reflect the fact that these practices reduce, but do not completely eliminate, the risk of disease transmission. In recent years, the term "sexually transmitted infections" (STIs) has been preferred over "STDs", as it has a broader range of meaning; a person may be infected, and may potentially infect others, without showing signs of disease.

Safe sex practices became more prominent in the late 1980s as a result of the AIDS epidemic. Promoting safe sex is now one of the aims of sex education. Safe sex is regarded as a harm reduction strategy aimed at reducing risks. The risk reduction of safe sex is not absolute; for example the reduced risk to the receptive partner of acquiring HIV from HIV seropositive partners not wearing condoms to compared to when they wear them is estimated to be about a four- to fivefold. Although some safe sex practices can be used as contraception, most forms of contraception do not protect against all or any STIs; likewise, some safe sex practices, like partner selection and low risk sex behavior, are not effective forms of contraception.

Safe sex is effective in avoiding STDs only if both parties involved in sexual intercourse agree on it and stick to it. During sexual intercourse using a condom, for example, the male could intentionally pull off the condom and continue penetrating without the female (or male receptive) partner's consent and notice. This is a high risk behavior that betrays trust as well as spreading disease.