The following levels, slightly modified, are defined in: Guidelines for the Formulation of Collection Development Policies, David L. Perkins, editor (Collection Development Committee, Resources and Technical Division, American Library Association, 1979). They incorporate and expand upon those formulated in: "American Library Association Guidelines for the formulation of collection development policies," Library Resources and Technical Services, Vol. 21, no. 1 (Winter 1977) pp.40-47.

A collection in which a library endeavors, so far as is reasonably possible, to include all significant works of recorded knowledge (publications, manuscripts, other forms), in all applicable languages, for a necessarily defined and limited field. This level of collecting intensity is that which maintains a "special collection"; the aim, if not the achievement, is exhaustiveness.

A collection which includes the major source materials required for dissertations and independent research, including materials containing research reporting, new findings, scientific experimental results, and other information useful to researchers. It also includes all important reference works and a wide selection of specialized monographs, as well as a very extensive collection of journals and major indexing and abstracting services in the field.

A collection which is adequate to support the course work of advanced undergraduate and master's degree programs, or sustained independent study; this is, which is adequate to maintain knowledge of a subject required for limited or generalized purposes, of less than research intensity. It includes a wide range of primary resources, basic monographs both current and retrospective, complete collections of the works of more important writers, selections from the works of secondary writers, a selection of representative journals, and the reference tools and fundamental bibliographical apparatus pertaining to the subject.

A collection which supports undergraduate or graduate course work, or sustained independent study; that is, which is adequate to maintain knowledge of a subject required for limited or generalized purposes, of less than research intensity. It includes a wide range of basic monographs, complete collections of the works of important writers, a selection of representative journals, and the reference tools and fundamental bibliographical apparatus pertaining to the subject.

A collection which is adequate to support undergraduate courses. It includes a judicious selection from currently published basic monographs (as are represented by Choice selections) supported by seminal retrospective monographs (as are represented by Books for College Libraries); a broad selection of works of more important writers; a selection of the major review journals; and current editions of the most significant reference tools and bibliographies pertaining to the subject.

A highly selective collection which serves to introduce and define the subject and to indicate the varieties of information available elsewhere. It includes major dictionaries and encyclopedias, selected editions of important works, historical surveys, important bibliographies, and a few major periodicals in the field.

A subject area in which few selections are made beyond very basic works.

The subject is not collected.