The correspondence in the Leonard Bernstein Collection consists of more than 17,500 individual items from over 3,300 individuals or organizations. All material from or relating to a correspondent is housed in its own folder(s) and arranged chronologically. Undated material is filed at the back. Each identifiable correspondent is indexed alphabetically in the finding aid along with the date range and the number of items in the folder(s). Unidentified correspondence is at the end. Most of the correspondence falls between the dates of 1932, the year of Bernstein's engagement of Helen Grace Coates as piano teacher at the age of 14, and 1990, the year of his death.

In addition to such standard items as letters, postcards, telegrams, and birthday and greeting cards, the correspondence also contains the occasional photograph, music manuscript, diary, appointment book, script, collection of poems, or art work (e.g., sketches). No attempt was made to indicate all the non-standard items where they occur, but on occasion a parenthetical note will be found regarding such novelties.

Most of Bernstein's individual correspondents are filed under their own names. However, some are filed under organizational or business names, or topics, e.g., . These designations pre-date the Library of Congress Music Division's possession of the material. Some letters from prominent individuals were moved from the "fan mail" collection to "correspondence" prior to the presentation of the collection to the Library.

A significant amount of the correspondence includes Bernstein's responses to the letters he received. These typically appear in the form of handwritten or typed replies in the margins or on the backs of the letters received by Bernstein. The handwritten responses are either in Bernstein's hand or that of Helen Coates in her capacity as secretary. There is no indication in this finding aid where such responses occur. In some cases, however, Bernstein's actual outgoing letters--either originals, or photocopies--are present, either filed chronologically within the correspondence, or collected separately in their own folder. In both instances, parenthetical notes indicate the filing method (for example, Burton Bernstein, Felicia Bernstein, Helen Coates, Serge Koussevitzky). After Bernstein's death, Charlie Harmon and Harry Kraut contacted people likely to have received letters from Bernstein and requested photocopies of that correspondence. These photocopies are filed at the end of each correspondent's folder. The only clue to the location of these items in the correspondence is found by noting the date spans--as these items were solicited via a letter dated post-1990 (also included)--most date spans which exceed 1990 indicate the presence of photocopied Bernstein correspondence.

In addition, the Library included two other sets of material in the Correspondence: over 300 condolence letters sent to Bernstein after the death of his father, referenced under Bernstein, Samuel J.; and over 700 letters, referenced under Coates, Helen, primarily from Bernstein to Coates, but also from various other persons to Coates, from Coates to Bernstein, and from Bernstein to several other persons. In the case of Helen Coates, each of the correspondents found in her file is listed parenthetically following her name in the guide with cross-references listed under the correspondent. For Samuel Bernstein's condolence letters, no cross references are provided.

In December 2010, the Leonard Bernstein estate donated over 1800 additional pieces of personal correspondence to the Library of Congress. Though much of this material is intensely personal and had been previously sealed, the family felt that since Bernstein has been dead over twenty years, the research value of the correspondence outweighed most of the privacy concerns. This additional correspondence has been physically added to the end of the series in boxes 60A-J, but the names are arranged alphabetically and interfiled with the previous correspondence in the finding aid. The hundreds of letters from dozens of correspondents include 79 additional letters from Felicia Bernstein, 101 from Shirley Bernstein, 37 from Helen Coates, 39 from Aaron Copland, 150 from David Diamond, 67 from Martha Gellhorn, 15 from Lillian Hellman, and 78 from David Oppenheim.

Many other series in the collection contain correspondence. In fact, "Fan Mail" and the "Personal Business Papers" under the Business Papers series are almost entirely correspondence, but even "Photographs" and "Writings" contain a certain amount--although the letters in the former are primarily addressed to members of Bernstein's staff, and letters in the latter include drafts of letters by Bernstein, some of which were never sent, and originals of letters sent by Bernstein (some of which appear to have been retrieved for inclusion in his book .)

Bernstein's family and staff were exceptional custodians of the correspondence prior to its coming to the Library and most of the organization and identification of materials was theirs. They have also always been responsive to questions that have come up during the course of our work, especially an attempt to identify as much of the unsigned, illegible, or sans surname signatures as possible. Special gratitude is due to Albert Tucker, who performed most of the work on the correspondence in the collection and prepared the following inventory.