The Membership subseries (0.84 linear feet), arranged alphabetically within each year, primarily consists of correspondence and statistics concerning ACLU membership. The correspondence includes comments on various issues concerning ACLU actions, applications, resignations, deaths, and membership surveys. The statistics include numbers of members and information on contributions.

The affiliates subseries (56.70 linear feet), arranged chronologically by year then alphabetically by state, contains mailings from the national office to affiliates, board minutes of affiliates, general correspondence, and affiliate publications. In states with several chapters, material is filed by city or chapter name within each state. In the early years many states had civil liberties committees but not full fledged affiliates. These files are labeled "committee."

This subseries (18.48 linear feet) documents civil liberties concerns within various states and U.S. Possessions. There are also a few folders documenting civil liberties concerns in Canada. Prior to creating a state affiliate network, the ACLU had "state correspondents"--individuals who monitored civil liberty concerns within their state and informed the national office of local cases and issues. More extensive for earlier years, prior to the growth of the state affiliates, the files are organized chronologically and then alphabetically by state within each year. Large cases or issues of concern are contained in their own folders; many minor issues are grouped a general folder for each state. Correspondence comprises the majority of this subseries, but briefs and printed matter are also found.

The Attacks and Commendations subseries (3.78 linear feet) documents attacks leveled against the ACLU by the press, various institutions, and individuals, as well as commendations of the ACLU, with the majority of the material dating to the early 1950s. The material is arranged in two sections: Attacks, arranged alphabetically by attacker, and Commendations, arranged chronologically. The attacks material consists of newspaper clippings, statements detailing the attacks themselves, correspondence between ACLU members, and correspondence between the ACLU and their attackers. The material also contains detailed documentation of the ACLU's response to each attack. Occasionally there are descriptions of the reaction to those responses, on the part of both the public and the attackers themselves.