In U.S. research libraries the level or depth of how much is collected on a particular subject can range from "basic" to "comprehensive," with "research" and "advanced study" as intermediate levels. As used in this manual:

1. Basic is the level needed for an undergraduate program or for general academic readers. Collecting is highly selective but includes major dictionaries and encyclopedias, important bibliographies, and a few important journals;
2. Advanced Study indicates what is required to support a master's level program;
3. Research level collecting is required for adequately supporting doctoral and more advanced research;
4. Comprehensive collections aim to acquire all significant and relevant materials in all formats, including manuscripts. Very few libraries can afford to collect comprehensively in any area.

UWM supports a number of doctoral programs and many masters level programs, in addition to a wide array of undergraduate majors, interdisciplinary programs, and a number of specialized centers, some of which the UW Board of Regents has designated "centers of excellence." Advanced study collections can be expected for the support of all graduate programs, and research level collections are needed to support research at the doctoral level and beyond.

The designation of a collection level is meant to provide a general benchmark for what should be found in the collection; it is not necessarily a claim that the collection has been assessed and evaluated at that level and it is not linked to specific titles or works. It is meant to serve as one measure of any future evaluations of parts of the libraries' collections.

Since there is a very large undergraduate enrollment at UWM, it is essential for the libraries to support undergraduate studies with a considerable amount of basic or general materials.

Academic departments have research and teaching interests and strengths in various specializations or sub-disciplines. Acquisitions need to reflect those interests and strengths, rather than consuming scarce financial resources and shelf space with large numbers of expensive and specialized materials on subjects which are not of interest to UWM's academic community. This implies a process of continuous adjustment in collection procedures, as research and teaching patterns change.

The curricula of some UWM academic departments offer broad and uniform coverage of their disciplines. In such cases the libraries strive to collect in-depth resources throughout the field. Alternately, a department may promote advanced research in some specialties, but offer only basic survey courses in others.

There are significant differences between the humanities, social sciences, the physical sciences, and the professional disciplines with respect to the kinds of materials needed. For instance, in the humanities disciplines books tend to be emphasized more than current journals, and books tend to retain their scholarly value far longer than is the case in the social or natural sciences. In the physical sciences current journal articles are more urgently needed than books, which tend to be more general or retrospective in nature.

The libraries monitor the numbers of books acquired in support of the various disciplines and sub-disciplines pursued at UWM.

Most of the materials collected are in English, but works in other languages are collected as appropriate and as funds permit. Clearly, such fields as Latin American Studies, Comparative Literature, Classics, Hebrew Studies, and the other languages and literature studies at UWM will require both texts and criticism in other languages. International studies may require books in Chinese, Japanese, and Arabic, even though these books may be difficult to catalog. Other subjects, such as Engineering or Physics, may require works in German or Russian.

Generally, for space and budget reasons, the libraries acquire only single copies of works. Exceptions to this practice apply to:

1. UWM authors' books, usually acquired for Special Collections as well as for the general stacks;
2. other works requiring a non-circulating copy in Special Collections, Archives, or the American Geographical Society Library, and a general stack copy;
3. standard works frequently on Reserve;
4. books much in demand by reason of public discussion;
5. books of more than usual continuing interest for which a queue of circulation "holds" has developed;
6. audiovisual materials in high demand;
7. classics in literature or in other fields, for which there is continuing interest over an extended period of time, and which may have a number of significantly different editions, in terms of text, critical matter, or both.

UWM faculty, staff, and members of the local community donate books, journals, manuscripts, and other materials which are a substantial benefit to the collections. The libraries add items of continuing academic value that are appropriate for the collections in terms of subject, treatment, physical condition, and other criteria. Books in poor physical condition are generally not added. Popular works of fiction or nonfiction, more suitable for a public library or personal collections, are not added. Generally such works are given to the Friends of the Library for their annual book sale, the proceeds of which are used to enhance the libraries' collections. Even when ostensibly "free," library materials require staff time to catalog and process. Works that are of marginal current usefulness and unlikely to be of significant use in the future may not be added. Likewise, older publications that once may have held significant interest, may not be sufficiently important today to justify the considerable expense of adding them to the collections. Decisions are made on an item by item basis.

It is in the nature of a research library that materials, once selected, are generally kept indefinitely, regardless of frequency of use. A seldom-used book may be precisely what a researcher will be looking for at some future time, and the item may be difficult to find except in a research collection. Such works are often significant in researching the history of a discipline. Although space may become scarce from time to time, physical expansion is preferable to discarding volumes simply because they no longer fit comfortably in existing facilities or because they are seldom used. However, materials in very poor physical condition which cannot economically be preserved or replaced, and which do not appear likely to be of significant research value, may be withdrawn from the collection. This decision is made easier if other copies of the work are known to exist in other libraries, and can be borrowed as needed.

Exceptions to the usual policy of keeping materials indefinitely may apply to certain items intended for practical use such as medical or nursing books containing obsolete information or advice that might actually be medically harmful, and without significant historical value. Decisions to remove such volumes should be made carefully, on a case by case basis, by subject experts.

Information that is better suited to another information medium will not be retained in an inappropriate form. For example, silent filmstrips may be replaced by CD-ROMS.

Old textbooks, of whatever sort, may be of little academic value, and may be discarded for that reason. Similarly, some outdated directories may no longer be of use.

Some special weeding criteria are applied to a few collections, e.g. Curriculum Library or Government Documents.

Textbooks tend to be of ephemeral rather than of lasting value, with some classic exceptions, and it is generally the responsibility of the individual student to acquire textbooks required for courses. Consequently, it is a policy of the libraries not to routinely purchase textbooks used at the university, particularly basic, lower-level texts. Some advanced or specialized upper-division texts do present information in ways that justify their purchase and may be acquired selectively.

Copies of UWM dissertations, Master's theses, and Senior Honors theses are collected. Theses and dissertations from other institutions are collected on a highly selective basis, according to expressed UWM program requirements.