A sex strike (sex boycott), or more formally known as Lysistratic nonaction (a nod to the Ancient Greek comedy Lysistrata), is a method of nonviolent resistance in which one or more persons refrain from or refuse sex with partners until policy or social demands are met. It is a form of temporary sexual abstinence. Sex strikes have been used to protest many issues, from war to gang violence to policies.

The effectiveness of sex strikes is contested.

The most famous example of a sex strike in the arts is the Greek playwright Aristophanes' work Lysistrata, an anti-war comedy. The female characters in the play, led by the eponymous Lysistrata, withhold sex from their husbands as part of their strategy to end the Peloponnesian War.

Among the Igbo people of Nigeria, in pre-colonial times, the community of women periodically formed themselves into a Council, a kind of women's trade union. This was headed by the Agba Ekwe, 'the favoured one of the goddess Idemili and her earthly manifestation'. She carried her staff of authority and had the final word in public gatherings and assemblies. Central among her tasks was to ensure men's good behaviour, punishing male attempts at harassment or abuse. What men most feared was the council's power of strike action. According to Ifi Amadiume, an Igbo anthropologist: "The strongest weapon the Council had and used against the men was the right to order mass strikes and demonstrations by all women. When ordered to strike, women refused to perform their expected duties and roles, including all domestic, sexual and maternal services. They would leave the town en masse, carrying only suckling babies. If angry enough, they were known to attack any men they met."

Citing similar examples of women's strike action in hunter-gatherer and other precolonial traditions around the world, some anthropologists argue that it was thanks to solidarity of this kind—especially collective resistance to the possibility of rape—that language, culture, and religion became established in our species in the first instance. This controversial hypothesis is known as the "Female Cosmetic Coalitions", "Lysistrata", or "sex strike" theory of human origins.

In April 2009 a group of Kenyan women organised a week-long sex strike aimed at politicians, encouraging the wives of the president and prime minister to join in too, and offering to pay prostitutes for lost earnings if they joined in.

In 2003 Leymah Gbowee and the Women of Liberia Mass Action for Peace organized nonviolence protests that included suggesting a sex strike, though this was not actually carried out. Their actions led to peace in Liberia after a 14‑year civil war and the election of Ellen Johnson Sirleaf, country's first female head of state. Leymah Gbowee was awarded the 2011 Nobel Peace Prize "for her non-violent struggle for the safety of women and for women's rights to full participation in peace-building work."

In October 2014, Pricilla Nanyang, a politician in South Sudan, coordinated a meeting of women peace activists in Juba "to advance the cause of peace, healing and reconciliation." Attendees issued a statement which called on women of South Sudan "to deny their husbands conjugal rights until they ensure that peace returns."