Subseries consists of correspondence between Cornell and friends, artists, dealers, collectors, galleries, museums, admirers, individuals whom he admired or with whom he was especially preoccupied, "helpers," and charitable institutions. Included are letters (in some instances, with photographs or poems enclosed), postcards, and greeting cards, as well as some art work, three-dimensional objects, and artifacts. Also included are some notes and printed material, such as newspaper and magazine clippings, pamphlets, brochures, publications, and publicity material, pertaining to individuals, institutions, and/or topics in which Cornell had a particular interest.

Correspondence documents some of Cornell's activities involved in creating his art work, such as his practice of using multiple copies of a single image in many of his works (as in a letter from John Allen referring to Cornell's order for multiple prints of a Loie Fuller image); his early attempts to advertise his art work (as in letters from the Blaker Advertising Agency, Columbia Records, Inc., and N. W. Ayer and Son); and his later, oftentimes hesitant, transactions with galleries and dealers, including Irving Blum, Charles Egan, Richard Feigen, Julien Levy, Robert Schoelkopf, and Eleanor Ward ( Series 1). Correspondence relates to the sale of his art work to galleries and individual collectors, and the exhibition of his art work in museums, including the Cleveland Museum of Art, Guggenheim Museum ( Diane Waldman and Tom Messer), Pasadena Art Museum, and Whitney Museum ( John Baur).

The positive reception of Cornell's art work is documented in many letters from admirers (including poet, Paul Carroll, who wrote two poems about Cornell's art work, the Fourth Grade Class at Murray Avenue School, actress, Eva Marie Saint, and author, Glenway Wescott, among others). The critical reception of Cornell's art work is documented in the many letters from people who have written or express interest in writing an article about Cornell (including Howard Griffin from , David Bourdon from magazine, and Brian O'Doherty, author of , among others).

Correspondence also concerns some of Cornell's major "explorations," including ones on the singers, Maria Malibran and Giuditta Pasta (as in letters from the English scholar, Richard Coe), and the ballerina, Fanny Cerrito (as in letters from Lillian Moore). Correspondence relates to his other research and collecting activities and includes numerous letters responding to his requests for information and/or material from institutions, such as the Harvard College Library, dealers, such as C. and I. K. Fletcher, and individuals, such as Marian Hannah Winter.

Correspondence documents Cornell's preoccupations with certain dancers (such as Allegra Kent, Tanaquil LeClerq, and Tamara Toumanova), actresses (such as Lois Smith), artists (Lee Bontecou), and other young women; his relationships with other artists, both young and established, including Piero Dorazio, Ray Johnson, Hubert Kappel, Roberto Matta Echauren, Dorothea Tanning, and Pavel Tchelitchew, among others; and his friendships and shared interests with individuals, such as Wayne Andrews, Charles Henri Ford, Parker Tyler, Donald Windham, and Marian Hannah Winter (their letters often entailing an exchange of ideas on topics such as literature, music, dance, art, and the pleasures of collecting). Correspondence also documents his generosity (in terms of gift giving) toward his friends (and their children) and individuals whom he admired (as in letters and notes of thanks for gifts of art work from Valerie Adams, George Bennette, Lee Bontecou, Susan Sontag, Jessica Tandy, and Tamara Toumanova, among others); and his generosity toward institutions providing public services to the less fortunate (as in letters acknowledging and expressing gratitude for donations from the New York Institute for the Education of the Blind and the Bedside Network, among others).

General correspondence is arranged in files according to correspondent and then alphabetically according the surname of the individual or the name of the institution. Items are arranged in rough chronological order within each file. When only a few items (typically less than three) are associated with a correspondent, these are arranged into general alphabetical files. Unidentified and miscellaneous items are arranged into files at the end of the subseries.