As a national library and the library of record for biomedicine in the United States, NLM builds its collection for the long term. With few exceptions, the Library retains material it acquires, although not necessarily in its original format. As collection development policies change over time, NLM does not remake the collection in the image of the newer policy.

In some instances, the Library may remove materials from the collection, according to the following guidelines:

1.

Withdrawal is the removal of a title from the NLM collection. Withdrawal follows a prescribed and rigorous review process. Justification for and approval of withdrawal is formally recorded in the Library's catalog.

a.

General withdrawal principles. Withdrawal may be recommended on one or more of the following grounds:

• Subject: Under current and former collecting policies, the work is not within the subject scope of the NLM collection. It may fit more properly within the collecting responsibility of another institution.
• Coverage: The work does not meet coverage criteria for the collection.
• Electronic availability: A free electronic work selected for the NLM collection that is not archived at NLM or in an identified repository may become permanently unavailable on the web.
• Deterioration or damage: The print, audio or visual content has deteriorated to the extent that copying or retention is not practical, and replacement with a better copy is not feasible.
• Loss: The work is no longer available.

b.

Withdrawal of audiovisual and electronic works on physical media. The long-term value of some audiovisual and electronic works on physical media may be difficult to determine at the time of selection. Changes in technologies, resources, and user demands may warrant the revisiting of some earlier selection decisions. Withdrawal of such works also may be based on the following grounds:

• Significance or relevance: The audiovisual or electronic work is of lesser significance or relevance compared with other works held in the subject or genre.
• Representation: The Library holds more audiovisual or electronic works than is judged necessary to represent the subject area or genre.

2.

Weeding is the removal of surplus copies, or supplementary material acquired for temporary, onsite use. Except for rare and valuable materials, the process is less rigorous than the withdrawal process. The following categories of material are candidates for weeding:

• Duplicate copies: Duplicate copies are candidates for weeding when the level of use no longer justifies their retention, or when a copy or copies of a particular work are inferior to other copies of that work held at NLM.
• Publications that are cumulated: After cumulated volumes (e.g., of bibliographic and reference works) are received, NLM may weed the now-superseded individual issues.
• Obsolete or less desirable formats: If a work is held in multiple formats, NLM may consider weeding the format that is less desirable from an access or preservation viewpoint.

3.

Removal or deletion of content may occur under very limited circumstances:

• Content offered during a public health emergency: The Library may collaborate with publishers and other organizations to expand access to relevant materials during a public health emergency. Once the emergency expires, and depending on license or other agreement terms, the content may be restricted or removed.

4.

Disposal is the physical process of properly disposing of items withdrawn or weeded from the collection. NLM has statutory authority (42 USC section 286) to discard materials from its collection, but prefers, whenever possible, to make withdrawn or weeded material available to another institution where the material would more appropriately reside. When material is no longer useable because of condition or obsolescence, it may be discarded.