The Andre Kostelanetz Collection includes materials related to Kostelanetz's career as a conductor and arranger of popular and classical music for radio broadcast, commercial recordings, and concert performance. It contains orchestral arrangements, correspondence, subject files, programs, clippings, scripts, cue cards, and photographs spanning from 1922 to 1984, with the bulk of materials dating from 1935 to 1979.

Most scores in the collection are arrangements of popular and symphonic music for Kostelanetz's orchestra that were performed for various radio programs in the 1930s and 1940s and for numerous commercial recordings from 1940 to 1979. Materials in the Orchestral Arrangements subseries include manuscript full scores prepared by an arranger or copyist and annotated by Kostelanetz, as well as complete part sets for orchestra. Some of these folders also contain photocopied or printed scores. Many parts folders also include a printed condensed score or photocopy of the manuscript production score. The Personal Music Library subseries includes printed scores annotated by Kostelanetz for possible orchestral performance, as well as reproductions of unpublished or rare scores found in his personal library.

The Correspondence series consists of letters, telegrams, and postcards to and from Kostelanetz's personal and professional contacts. Also included are letters from fans of his radio broadcasts and recordings, and from musicians hoping to be featured in his concerts. Notable correspondents include Harold Arlen, Irving Berlin, Leonard Bernstein, Aaron Copland, Ira Gershwin, Jerome Kern, Serge Koussevitzky, Eugene Ormandy, Richard Rodgers, Leopold Stokowski, and Arturo Toscanini. The collection also contains correspondence with several major political and cultural figures of the mid-twentieth century, such as Fred Astaire, Jimmy Carter, Madame Chiang Kai-shek, Mamie Eisenhower, General Douglas MacArthur II, Edward R. Murrow, Ogden Nash, Richard Nixon, and Carl Sandburg. Particularly noteworthy among these are a letter from Aaron Copland to Kostelanetz recommending the musical services of a then-unknown Leonard Bernstein, followed by a letter from Bernstein requesting a meeting with Kostelanetz; extensive correspondence from Eugene Ormandy (one of Kostelanetz's teachers) containing advice on conducting; and notes between Ira Gerswhin and Kostelanetz regarding a possible collaboration with George Balanchine on a ballet.

Subject files in the collection contain documents from Kostelanetz's professional and personal life. These include programs for concerts not featuring Kostelanetz, correspondence and notes regarding the performance of particular works, documentation of club and union memberships, wardrobe, arrangements, awards, and special events, as well as financial and medical records. The series also contains files related to Kostelanetz's research in the field of acoustics and materials for his autobiography, Echoes, which was published posthumously. Especially noteworthy are the extensive notes from Aaron Copland, Jerome Kern, and Virgil Thomson surrounding the Portraits of Great Americans pieces that Kostelanetz commissioned in 1942, including Copland's A Lincoln Portrait.

Kostelanetz's career as a guest conductor for numerous orchestras around the world and as a regular conductor of the New York Philharmonic is documented in the Concerts and Tours series. Materials include box-office reports, itineraries, program drafts, published programs, newspaper reviews, and contracts, as well as correspondence to and from Kostelanetz's agents. Some letters document discussions between Kostelanetz and soloists' agents regarding appropriate pieces for encores. Most of Kostelanetz's concerts during the 1930s and 1940s featured Lily Pons as a soloist.

Kostelanetz was well-known for his radio broadcasts in the 1930s and 1940s. The Radio series contains materials related to Kostelanetz's work as a conductor for programs on the CBS network sponsored by Liggett & Myers Tobacco (The Chesterfield Hour), Coca-Cola (The Pause That Refreshes), Ethyl Gasoline (Tune-Up Time), and Chrysler (Music Millions Love). Included are letters between Kostelanetz, radio producers, and sponsors, as well as rosters of orchestra and chorus members, contracts, print advertisements, scripts, and photographs. Also found here are listings for individual broadcasts, including date, repertoire, and names of performers. An additional series, Television and Motion Pictures, contains materials pertaining to Kostelanetz's work for film soundtracks and television broadcasts. These include correspondence, notes on program ideas, cue cards, scripts, shooting schedules, and photographs.

The Recordings series contains documentation related to the dozens of studio recordings Kostelanetz made for Columbia Records. The general files include correspondence, royalties, promotional material, contracts, displays for record stores, Columbia Records catalogs, and brochures. Especially noteworthy are letters between Kostelanetz and Columbia Records staff regarding promotion of his albums and the state of the classical music market. Also included are materials related to Kostelanetz's field recordings in Southeast Asia in 1955 and his work with Brunswick Records. The recording session files include take sheets, rosters of performers, schedules, and other documentation about particular albums.

The collection includes substantial material related to Kostelanetz's first wife, soprano Lily Pons. The series bearing her name contains correspondence, financial and legal documents, clippings, and photographs related to Pons from 1935 to 1959, roughly the period of her marriage to Kostelanetz. The series also includes numerous clippings documenting their divorce, as well as obituaries of Pons. Correspondence consists primarily of telegrams and handwritten letters from Pons to Kostelanetz, mostly in French.

During the Second World War, Kostelanetz and Pons took two four-month tours for the United Service Organizations (U.S.O.) to entertain American troops. The U.S.O. series contains correspondence, schedules, programs, newsletters, clippings, photographs, and other memorabilia. The first tour spanned May 9 until August 14, 1944, and included stops in North Africa, Iran, Egypt, Italy, and Israel. The second tour lasted from December 10, 1944, until April 11, 1945, and included India, China, Burma, Belgium, France, and Germany. The Press series includes clippings and advertisements documenting Kostelanetz's career, as well as clippings related to his acquaintances and personal interests. The scrapbooks are large volumes of clippings about Kostelanetz, including press materials from cities where he appeared as a guest conductor.

Kostelanetz's corrections, emendations, and notes to musical scores used in recording sessions and concert performances form another series in the collection. Corrections are handwritten on notebook paper and include both musical notation and lists of performance instructions. In some cases, corrections and ideas for improvement are written on recording session take sheets. Most include instructions to Kostelanetz's assistant, Lou Robbins, for incorporating the corrections into the full score.

The Photographs series contains both professional photographs and snapshots that document Kostelanetz's career and personal life from approximately 1935 to 1980. Particularly well-documented are his radio broadcasts and rehearsals in Liederkranz Hall, as well as his performances with various military orchestras during the early 1940s. There are also many snapshots from his 1974 trip to Southeast Asia and the Middle East. Numerous photos are inscribed to Kostelanetz from musicians and other famous acquaintances. A small series of realia rounds out the collection. Among these personal items are an oil painting of Kostelanetz, awards and honors, and three conductors' batons.