Lambda Legal Defense and Education Fund, better known as Lambda Legal, is an American civil rights organization that focuses on lesbian, gay, bisexual, and transgender (LGBT) communities as well as people living with HIV/AIDS (PWAs) through impact litigation, societal education, and public policy work.

Lambda’s founder William J. Thom, Esq. submitted incorporation papers for approval to the New York Courts in 1971, but his application was denied on the grounds that its proposed activities would be contrary to public policy. That decision was overturned in 1973 by the New York Court of Appeals, which is the highest court of New York State.

Because of the scarcity of openly gay lawyers in 1973, Lambda Legal formed a Board of Advisors of eminent New Yorkers sympathetic to the cause of gay rights. They included US Congressperson Bella Abzug, NY State Senator Carol Bellamy, Association of the Bar President Merrell E. Clark, Rev. John Corn of Trinity Church and Martin Duberman, Distinguished Professor at City University of New York. Also on the Board of Advisors were two lawyers who later became New York State Supreme Court Justices: Phyllis Gangel-Jacob and Shirley Fingerhood.

From its inception, Lambda Legal sought diversity on its board of directors. Initially it could find no lesbian lawyers who were willing or able to be openly associated with a gay activist organization. Nathalie Rockhill, a major figure in the early post-Stonewall days of Gay Liberation, was the first woman elected to the board in 1974. She was soon followed by lesbian law students and, in time, by lesbian lawyers. By the 1980s, men and women were equally represented on Lambda’s board.

Lambda’s growth paralleled the growth of the gay movement. By the 1980s, with the advent of AIDS, gay awareness and activism had grown significantly. Thomas B. Stoddard, who was executive director from 1986 to 1992, helped to author a bill passed in 1986 by the New York City Council to protect gays against bias in housing, employment, and public accommodations. Mayor Ed Koch signed the bill enacting it into law. In 1993, Stoddard and other national gay leaders met with president Bill Clinton, the first such delegation to meet inside the Oval Office.

In 2013 Lambda Legal – Midwest Regional Office was inducted into the Chicago Gay and Lesbian Hall of Fame.

Its national headquarters remain in New York City, but today it has regional offices in Atlanta, Chicago, Dallas, Los Angeles, and Washington.

Lambda Legal has played a role in many legal cases pertaining to gay rights, including the 6-3 United States Supreme Court’s 2003 decision in Lawrence v. Texas, which invalidated sodomy laws in the United States.

Lambda Legal carries out its legal work principally through test cases selected for the likelihood of their success in establishing positive legal precedents that will affect lesbians, gay men, bisexuals, transgender people and those affected by HIV.