Pederasty or paederasty (US: /ˈpɛdəræsti/ or UK: /ˈpdəræsti/) is a sexual relationship between an adult man and a pubescent or adolescent boy. The term pederasty is primarily used to refer to historical practices of certain cultures, particularly ancient Greece and ancient Rome.

In most countries today such relationships are illegal. The local age of consent determines whether a person is considered legally competent to consent to sexual acts, and whether such contact is child sexual abuse or statutory rape. An adult engaging in sexual activity with a minor may be considered abusive by medical authorities for a variety of reasons, including the age of the minor, the likelihood of the minor developing one or more mental disorders, such as posttraumatic stress disorder, physical injury to the minor, and the minor's propensity for further victimization in adulthood.