Strategic litigation, also known as impact litigation, is the practice of bringing lawsuits intended to bring about societal change. Impact litigation cases may be class action lawsuits or individual claims with broader significance, and may rely on statutory law arguments or on constitutional claims. Such litigation has been widely and successfully used to influence public policy, especially by left-leaning groups, and often attracts significant media attention. One prominent instance of this practice is Brown v. Board of Education.

In the late nineteenth and early twentieth centuries, the American Civil Liberties Union and National Association for the Advancement of Colored People (at times through its Legal Defense Fund) both pursued legal action to advance and protect civil rights in the United States. The ACLU followed a primarily "defensive" strategy, fighting individual violations of rights when they were identified. The NAACP, in contrast, developed a more coordinated plan to actively file suits to challenge discrimination, known as "affirmative" or "strategic" litigation. The NAACP's model became the pattern for "impact litigation" strategies, which applied similar tactics in contexts other than racial discrimination.

Important early impact litigation cases included Brown v. Board of Education and Roe v. Wade. Brown, a 1954 U.S. school desegregation decision, was carefully prepared by Thurgood Marshall and other NAACP lawyers so that the eventual Supreme Court ruling invalidated official racial discrimination throughout the U.S. government. Many cases since then have closely imitated it, in the course of seeking greater protections for other disadvantaged groups.

Impact litigation has played a major role in the development of American desegregation, women's rights, abortion, tobacco regulation policy and gay marriage.

Since the 1980s, impact litigation has been used to seek the reform of U.S. child welfare law, following earlier work which involved the courts in jail and mental hospital reforms, and in school desegregation.

Strategic impact litigation, among other things, has also been used in Nigeria to push for convictions of perpetrators of police brutality and to defeat legal attacks on the freedom of the press.

In a few jurisdictions where attorneys are prohibited from bringing class action lawsuits, citizens have filed "grassroots impact litigation" cases and successfully represented their own claims.

Impact litigation has been criticized by legal scholars and politicians on the basis of judicial legitimacy and competence.