Walter Nelles (1883–1937) was an American lawyer and law professor. Nelles is best remembered as the co-founder and first chief legal counsel of the National Civil Liberties Bureau and its successor, the American Civil Liberties Union. In this connection, Nelles achieved public notice for his legal work on behalf of pacifists charged with violating the Espionage Act during World War I and in other politically charged civil rights and constitutional law cases in later years.