A paternity suit is a legal action which is taken to determine the identity of the father of a child. There are a number of reasons to initiate a paternity suit, but most suits are filed to establish financial or moral responsibility on the part of one or both parents involved. A paternity suit may also be used to gain visitation rights, or to settle a contentious issue. Parents can also avoid a paternity suit by working out an amicable private agreement.

Several people can file a paternity suit. Mothers often file them to legally establish the identity of the man who fathered the child in question. This legal decision can be used to sue for child support and other benefits. A man may file a paternity suit to clear up his position in a case, and a child can file a paternity suit to find out who his or her father is. Certain government agencies may also initiate paternity suits, especially in the cases of contentious adoptions.

One of the best ways to establish paternity is a blood test, which may be ordered by the court if the parents cannot reach an agreement. If the blood test indicates that the man in question is not the father of the child, the suit is dismissed. On the other hand, the outcome of the test may indicate that the man is the father of the child, in which case the court will usually work with the parents to reach an agreement on custody, child support, and related issues.

In many cases, a paternity suit is filed by an unmarried woman. The husband in a married couple is presumed to be the father of any children born in wedlock, unless proved otherwise. A husband may use a paternity suit to prove a case of adultery and to potentially absolve himself of any financial responsibility towards a child who is not his.

Typically, a paternity suit is handled by a lawyer who specializes in family law such as divorce, mediation, and disputes over child custody and support. The lawyer usually has a serious discussion with the person filing the suit, to ensure that the suit has solid grounds and will not be viewed as harassment or a "nuisance" suit. Depending on the region in which the suit is filed, the suit may also be dealt with in family court, rather than in a general court. In some cases, mediation and other support services are offered through the court, in an attempt to resolve the situation amicably, no matter what the outcome of the case is.