Series 1, Correspondence (1897-1981) consists mainly of personal and business correspondence. Some of the documents are not letters per se, but they relate to correspondence Baldwin had and for this reason have been included in the correspondence series rather than with the subject files. This series gives a fairly complete picture of the diversity of Baldwin's interests, for his correspondence touched on all areas of his life. However, Baldwin had few long-term correspondents, perhaps detracting somewhat from the richness of the materials in this series.

One of the long-term correspondences Baldwin did maintain was with Charlotte Ryman, a woman who acted as a godmother figure for him during his teenage years and beyond. His first letters to her represent the earliest written papers of the collection, dating from 1897. Also from this era are letters from Baldwin's mother, Lucy Cushing Nash Baldwin. Baldwin corresponded relatively frequently throughout the 'teens and early twenties with Emma Goldman, the anarchist who greatly affected his political thinking. Other notable correspondences, though not as substantive, were with Eleanor Roosevelt, Upton Sinclair, Arthur Schlesinger, Jr., and Margaret Sanger. Other important names are also included in this series – Mahatma Gandhi, Edward R. Murrow, John Kenneth Galbraith, Felix Frankfurter, Douglas MacArthur, John F. Kennedy – but Baldwin's correspondence with these people was slight. Unfortunately, many of the more important people in Baldwin's life, including Norman Thomas, John Haynes Holmes, Ernest Angell, and Baldwin's family, are underrepresented in this series.

More substantial are official and subject-related correspondence. Documents relating to Baldwin's time in St. Louis, many of which deal with his years at the Juvenile Court and the book he wrote with Bernard Flexner about Juvenile Court procedures, are located in this series. All the materials from his year in prison are also included here. Other significant correspondences include papers relating to the debate over civil rights in Okinawa and the Ryukus Islands, to Puerto Rico, to the ACLU after Baldwin's retirement as executive director, to Baldwin's term as an Overseer of the Harvard Economics Department, and to the Robert Marshall Civil Liberties Trust, of which Baldwin was a trustee. Correspondence also exists from many of the organizations with which Baldwin had some sort of involvement, such as the International Fellowship of Reconciliation, the Inter-American Association for Democracy and Freedom, the American League for Peace and Democracy, Americans for Democratic Action, the National Conference of Social Welfare, and various organizations relating to Spanish democracy and refugees.

Of unexpected interest may be the "Academic Requests" files, which include Baldwin's responses to queries from academics about a wide range of topics, including the Scopes trial, pacifism, and the ACLU. These, like the "Miscellaneous" and "ACLU" files are organized chronologically by year, although in general no attempt has been made to organize the papers strictly in chronological order. Correspondences illuminating various views which Baldwin held are filed under the various subject headings, including "Gay Rights," "America," and "Israel-Palestine," to name a few. Occasionally, folders are grouped into subseries, which have then been filed alphabetically according to the subseries heading. The subseries in this series are Roger N. Baldwin, Birds, Communism, Harvard, India, Juvenile Court Matters, Political Prisoners, Prison, Puerto Rico, St. Louis Correspondence, State Conference of Charities and Corrections, and World Tour.