A sexual partner is a person with whom one engages in sex acts. Note that it is possible to have a sexual partner without having an intimate relationship, or even an acquaintanceship with that person; viz., casual sex, or sex with a prostitute.

A person may have one, none, or more than one sexual partners at any one time, and this pattern may change throughout life.

Terms related to sexual partners include:

• virginity: the state prior to having a sexual partner; a small minority of people remain virgins throughout life
• monogamy: having a single long-term sexual partner
• marriage: officially committing to a single sexual partner (traditionally of the opposite sex, but attitudes to this are changing in some places)
• sexual infidelity: having a sexual relationship outside of a relationship that includes a commitment to have no other sexual partners
• sexual fidelity: not having other sexual partners other than one's committed partner, even temporarily
• serial monogamy: having a series of monogamous relationships, one after the other
• polygamy: having multiple long-term female sexual partners (strictly speaking this should be called "polygyny"; polygamy also includes polyandry)
• polyandry: having multiple long-term male sexual partners
• polyamory: encompasses a wide range of relationships, including those above: polyamorous relationships may include both committed and casual relationships
• sexual promiscuity: having casual sexual partners at will (compare with chastity)

Variations between cultures

Different cultures have different viewpoints and levels of tolerance for the different patterns of sexual activity.

The most common patterns in Western society are monogamy, serial monogamy and marriage. Polygamous and/or polyandrous marriage is typically not found in Western culture, except in specific minority religions, and is illegal in many places. However, sexual promiscuity is commonly accepted, and a minority have open relationships or practice polyamory.

Polygamy is permitted in Islamic culture, and both polygamy and polyandry are found in African culture.