This series includes the correspondence of the ACLU on a variety of matters that are not found elsewhere in the collection. Major topics addressed include aliens, amnesty, attacks on the ACLU, deportations, Indians, IWW cases, international civil liberties, organized labor, minority political party rights, Negroes and civil rights, patriotic organizations and their attacks on the ACLU, propaganda for and against civil liberties, race relations and discrimination, radio, religious freedom, sedition, and the United Nations.

Records in this series indicate the ACLU's vast correspondence with a variety of cooperating organizations around the nation and the world. Baldwin believed there was strength in numbers and his wide-ranging correspondence reflected a desire to work with other organizations on the variety of issues addressed by the ACLU. The series is arranged alphabetically by name of the outside organization. These organizations focused on such subjects as anti-Fascism, protection of aliens, civil rights, conscientious objection, pacifism, Communism, socialism, and religion.

Beginning in 1936 the ACLU formed a quasi-independent New York City Committee to handle local matters. Eventually this organization became one of the most important local affiliates in the country, namely the New York Civil Liberties Union, but not before Baldwin's retirement in 1950. These records document the internal activities of this committee as well as its many special interests which included limits on free speech and assembly, labor strikes, Communist activities, civil rights, police brutality, wiretapping and Works Progress Administration policies.