Ensemble librarianship (or performance librarianship) is an area of music librarianship which specializes in serving the needs of musical ensembles, including symphony and chamber orchestras, opera houses, ballet companies, wind ensembles and educational institutions. Ensemble librarians acquire printed music and prepare it for performance.

Ensemble or performance librarianship is a relatively new and evolving field with an oral history, so in many instances, there is no written history upon which to rely. Aside from a few surveys and recorded interviews, there are very few documents describing the history of the profession at this point in time. Historically, music librarians were only required to handle acquisitions and distribution—they did not have the requirements many librarians have today to mark individual parts for performance, correct errors, work in close consultation with the music director and/or artistic staff, and conduct scholarly research. Traditionally, many orchestra librarians were string players, since they already possessed a working knowledge of bowings (markings made in string parts). "Until 1970s, in all but the largest orchestras the librarian had a playing position in the orchestra and engaged in part time library work to supplement his or her income. In other cases the librarian had retired from playing and still wished to remain a part of the orchestra." A survey at the 1998 annual conference of the Major Orchestra Librarians' Association (MOLA) revealed that "in some smaller orchestras ..., the library position had remained part-time for the most part until the mid 1980s to early 1990s." In some organizations, librarian duties were alternatively fulfilled by an administrative staff member (i.e. personnel manager or orchestra manager) and this is still the case with many smaller organizations today. Gradually, particularly with the larger orchestras and bands, the role of music librarian has become a job obtained on an audition basis and which requires the demonstration of extensive knowledge of not only music notation, history, and performance practice, but also specialized technique and research ability. Today, larger and more established organizations can have multiple librarians and a hierarchy has developed, where a principal librarian is often identified and compensated accordingly (much like principal string or wind/brass/percussion players in an orchestral setting). This principal librarian may then work with one or more assistant librarians and can delegate tasks.

A professional ensemble librarian requires a diverse and extensive musical, research, and often administrative-oriented background. Currently, there is no formal degree program specifically for ensemble or performance librarianship offered at any academic institution. Consequently, primary forms of training include degree programs or their equivalent in music performance (instrumental), music theory, musicology, or related fields, in conjunction with mentoring, internships, and on-the-job training. In the United States, work as an apprentice with a career librarian is a common and invaluable educational tool. Some ensemble librarians hold degrees in library science (LIS, MLIS). "Most music schools and many library / information science schools have programs that offer a variety of related course work which could be applied to orchestra librarianship." While such experience can be very helpful, this is not typically a specific requirement to work as an ensemble librarian. Ideally, "training for orchestra librarianship should include a broad and intensive education in all aspects of music and the liberal arts. This career requires a combination of formal education and extensive practical experience in a symphonic organization."

Quoted with permission from Russ Girsberger's "A Manual for the Performance Library":

The following list describes the qualifications that are desirable to function successfully as a performance librarian. Not every position requires all of these abilities, but professional performance librarians use these skills on a regular basis in their work.

In the U.S., some professional ensemble librarians must now endure a process similar to instrumental orchestral auditions in order to obtain their jobs. "Marcia Farabee (Principal Librarian, National Symphony) explains that today some orchestras have adopted a similar audition process for librarians. These 'librarian auditions' involve interviews as well as written tests which ask questions to which a qualified candidate should know the answers." Experience, formal education, and references provided on the auditionee's résumé play an important role, but the candidate may be required to pass this live audition and interview component, as well. As noted, larger orchestras and the more prestigious summer fellowships may require a candidate to pass a written exam demonstrating knowledge of composers, important historical facts, publishers, and repertoire. Librarians wishing to pursue this career study long hours in order to prepare for these auditions and therefore, professional ensemble librarianship is becoming a competitive field in North America. In Europe, many ensemble librarians currently obtain their positions via a more standard job interview process.

The ensemble librarian is often the primary individual responsible for research, acquisition (via purchase, rental, commission, or lending), receipt of materials, and cataloging of performing materials (scores and parts) for a musical organization. The librarian consults and collaborates with the music director, other artistic or administrative staff members, and/or soloists to identify the correct edition or version of the work to be acquired and its source, then works to determine its cost, delivery time, method of delivery, and any other associated concerns. The librarian may also be responsible for locating and obtaining perusal materials (scores and/or recordings for study). An important component of the acquisition process, particularly in the case of renting works under copyright, can be obtaining permission and licensing for any recording, broadcast (radio or World Wide Web), or other types of mechanical use that may be planned.

Following the purchase or commission of performance materials, the librarian may be obligated to create and/or maintain a catalog of the musical organization's physical holdings of performance and reference material. This can be as simple as an itemized listing of materials owned or as complex as designing and implementing a custom-made electronic catalog for the ensemble. Many organizations utilize pre-existing database programs such as OPAS. Upon receipt of purchased or donated materials, the librarian inventories the scores and parts, stamps or otherwise marks them with the organization's name and identifying information, and prepares them for storage. Cataloging can also extend to maintaining a record of conductor markings and dates of use, condition of materials, and performance and lending history.