In the context of libraries and archives, an inventory refers to a detailed list or record of the items, materials, or resources held within a collection.

It helps to document and organize the contents, making it easier for staff to manage, locate, and track items. An inventory typically includes information such as titles, authors, publication dates, call numbers, and other relevant details about each item in the collection. It is the one method that libraries and archives use to determine whether some items in their collection are in need of preservation or conservation activities. A modern inventory might involve examining item by item with a barcode scanner and a laptop, with the objective of adjusting bibliographic and item records in theirs and OCLC's WorldCat databases. Using a laptop and handheld bar code reader will "reduce human error and inconsistencies, while helping to maintain staff concentration and enthusiasm for the project".

Print materials in the digital age, though dramatically decreased in size compared to e-print materials, are still valuable components of a library's collection. Increasing print material's accessibility, and reducing user frustration, make the inventory process an effective tool in improving library service quality. "When library users are unable to find materials in the expected locations, they lose confidence in the library catalog as well as in the library itself". Missing or mislabeled books have a direct impact on the quality of library services. Maintaining the stacks through inventories and shelf reading can mitigate staff time lost searching for missing or mislabeled items.

Libraries have thousands of books; large academic libraries may have millions of books. Doing an annual (or less frequent) physical inventory with the laying on of hands on each individual item may not be practical for several reasons. It may not be financially feasible, employees required may not have extra time to devote to such an inventory, and there are no financial rewards for the Library for completing an inventory. Problems that are discovered (books in need of repurchase, rebinding, repair, or digitization) may require solutions that are expensive and labor-intensive. Because of these restraints, inventories may not take place for decades, if ever, at large academic institutions. By contrast, complete inventories are often a regular part of the school library media specialist's job at K-12 institutions, where inventory may be a legal requirement that shows that the libraries are accountable for the money they have spent throughout the year. Checking for lost books and materials can be similarly compared to auditing.

However, there are alternative options to performing a complete inventory, such as performing a selective inventory. Selective inventory can be performed by circumstance or by data prediction. Physical space is a premium in libraries. Inventorying mini collections before relocating them to their new location presents the library with an opportunity to perform a selective inventory project. An alternative to opportunistic selective inventory projects is Kohl's (1982) assertion that circulation statistics, book search statistics, and ILL statistics can be useful tools in identifying areas as possible selective inventory areas. He writes, "areas in need of an inventory can be identified through the use of predictive data". Once the objectives for accuracy and methods of measuring have been established "the criteria need to be quantified. An overall measure of the inventory accuracy should be maintained as a management key performance indicator".

Although collecting new materials is viewed as a central mission of the library, maintaining the condition of library collections, which includes less satisfactory activities such as weeding, book repair, shifting and counting what libraries think they have on their shelves, are also a vital part of the library's mission to provide access to current patrons, as well as those people who will use the library at some point in the future.

Each time an inventory is conducted the physical condition of the collection and bibliographic representation problems are identified and addressed. "This enables the integrity of the OPAC to be strengthened, [making] it a more effective resource for users". Improved accessibility of collections for users has a tremendous impact on patron service and how the library is perceived. During an inventory process "library staff gain knowledge of the collection and are [better] able to provide stronger customer service." Patrons benefit from the confidence library staff gain in their collections and in their collection development skills. Inventories help guarantee that the collections as listed in Online public access catalogs and Finding aids do not lack integrity. School libraries also use the inventory to assess the collection (numbers, age and ratio:student) against benchmarks of accrediting institutions, and also to examine each resource and determine its future in the collection based on age, relevance, currency and condition—which may include repair, replacement, disposal or cleaning to ensure that attractive, up-to-date resources are available for patrons. Inventory can also identify anomalies in the catalog and provide an opportunity to correct catalog records and labeling of items. This is also a time when shelves can be rearranged to minimize overcrowding to prevent damage.

Sampling is a compromise measure, which can be an important management tool. Random sampling of library collections can give a quick and clear assessment measure of a collection—whether the books are present, and whether those books present are in good physical condition. In 1982, the California State University libraries, suggested inventory procedures to insure that the 19 campus collections were secure and intact. They recognized that a complete regular inventory was too expensive, and decided that the best method of assessing book loss would be to use sampling. Every three years, a sample was to be taken of an identified number of items in each Library of Congress letter classification. If loss rates were more than 1% for two years in a row, this would indicate that a full inventory was needed.