Forced fatherhood or imposed paternity, occurs when a man becomes a father against his will or without his consent. It can include deception by a partner about her ability to get pregnant or use of contraceptives, birth control sabotage, paternity fraud and sexual assaults of males that result in pregnancy.

"Sperm theft" (also known as "unauthorized use of sperm", "spermjacking" or "spurgling" (a portmanteau of sperm and burgling)), refers to a specific form of forced fatherhood in which a man's semen is used to impregnate a woman without his consent. Although the term uses the word "theft", it more closely falls under a state of fraud or breach of contract. Stealing of sperm in itself without using it for successful insemination is not illegal and is difficult to prove. It usually has no bearing on issues like child support. It is considered an issue in the men's rights movement.

Forced fatherhood falls into three main categories:

The prevalence of imposed paternity is difficult to measure. Research for the Centers for Disease Control and Prevention in 2011 found that approximately 10.4% (or an estimated 11.7 million) of men in the United States reported ever having an intimate partner who tried to get pregnant when they did not want to or tried to stop them from using birth control. In a survey of 5000 women for the British magazine That's Life, 42% stated that they would lie about using birth control in order to get pregnant, in spite of the wishes of their partner.

Forced fatherhood (namely a woman becoming pregnant against a man's will or without his consent) is not illegal anywhere. Cases are usually reported in connection with disputes over child support. When the obligation to provide child support is challenged by men who allege that their sperm had been stolen or otherwise used to inseminate a woman without their consent, courts will typically enforce the doctrine of strict liability: namely, that a man is liable to support a child conceived with his sperm, irrespective of the circumstances of conception, including any criminal conduct on the part of the mother. Plaintiff arguments of tort liability for fraud or misrepresentation typically do not hold up. Courts are also thought to be reluctant to remedy such grievances as it would mean ruling that a child was born as a result of deception. In some cases, a victim of sperm theft can sue the perpetrator for emotional trauma inflicted.

Myrisha S. Lewis has written that male victims of contraceptive fraud, sexual assault, and statutory rape should not be "punished with child support liability, but instead receive compensation for the unauthorized use of their biological products." She argues that the policy of strict liability unjustly penalises male victims of sexual assault. She contrasts their status with that of voluntary sperm donors, who are exempt from child support liability.

In a "landmark ruling" establishing the legal principle that a man's semen is his own property, Lord Chief Justice, Lord Judge, the most senior judge in England and Wales, ruled in favor of six unnamed men who sued the NHS for damages after their sperm samples were lost. The men were all cancer patients who had been advised to freeze their sperm due to the risk of chemotherapy damaging their fertility. Lord Judge, Master of the Rolls Sir Anthony Clarke, and Lord Justice Wilson ruled that the sperm samples were legally the property of the men, and dismissed the argument made by the NHS that the samples should be given the same status as discarded toenails or hair.

Steve Moxon has written, "it must only be a matter of time before the absurdity of 'sperm theft' is stamped upon. The position at the moment is that of a dam held back by 'the best interests of the child' concept, which is proxy for 'the best interests of the state' in not paying child support. It only takes one case to successfully assert the rights of the deceived man for the dam wall to break."