The Research Libraries Group developed a system of collecting levels, knows as the RLG Conspectus, intended primarily for the uniform evaluation of collections in research libraries. The use of these collecting levels evolved from a tool for evaluation into a meaningful set of descriptors employed in library collection policy statements. These levels are used in the Library of Congress policy statements to define the extent of the Library's collections. The general definitions of these collecting levels are:
- Out-of-Scope: The Library does not collect in this area.
- Minimal Level: A subject area in which few selections are made beyond very basic works. For foreign law collections, this includes statutes and codes.
- Basic Information Level: A collection of up-to-date general materials that serve to introduce and define a subject and to indicate the varieties of information available elsewhere. It may include dictionaries, encyclopedias, selected editions of important works, historical surveys, bibliographies, handbooks, a few major periodicals, in the minimum number that will serve the purpose. A basic information collection is not sufficiently intensive to support any courses of independent study in the subject area involved. For law collections, this includes selected monographs and loose-leaf titles in American law and case reports and digests in foreign law.
- Instructional Support Level: A collection that in a university is adequate to support undergraduate and most graduate instruction, or sustained independent study; that 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 works of more important writers, selections from the works of secondary writers, a selection of representative journals, and reference tools and fundamental bibliographical apparatus pertaining to the subject. In American law collections, this includes comprehensive trade publications and loose-leaf materials, and for foreign law, periodicals and monographs.
- Research Level: A collection that includes the major published 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 is intended to include 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. Older material is retained for historical research. Government documents are included in American and foreign law collections.
- Comprehensive Level: A collection which, so far as is reasonably possible, includes all significant works of recorded knowledge (publications, manuscripts, and other forms), in all applicable languages, for a necessarily defined and limited field. This level of collecting intensity is one that maintains a " special collection." The aim, if not achievement, is exhaustiveness. Older material is retained for historical research. In law collections, this includes manuscripts, dissertations, and material on non-legal aspects.