Websites, blogs, social media, collections of online documents, and other web content are born digital materials that play an increasingly important role in contributing to and documenting the scholarly biomedical record. They not only provide guidance to the biomedical community, but also may illustrate or synthesize a diversity of scientific, philosophical, and cultural theories, perspectives, or evidential sources in health and medicine. NLM selectively aggregates, maintains, and provides permanent access to web content, in accordance with NLM Selection Guidelines by Subject. Web content is collected to document a particular subject theme or event, to chronicle NLM institutional history, or to preserve scientific research, guidance, and diverse perspectives in a particular area of interest.

NLM's web collecting and archiving are primarily collection-based activities. Multiple web sites are generally collected as part of a broader theme, event or topic. NLM gives highest priority to content that is at risk of loss, or that is believed to be of vital interest to current and future NLM audiences and unlikely to be preserved elsewhere. The Library's goal is to collect and preserve selected web content at a particular point in time (i.e., snapshots or versions) or over a period of time (e.g., daily, monthly, or quarterly).

NLM collaborates with other organizations and libraries, including other Federal libraries, to collect and preserve web content which crosses institutional collecting boundaries.

NLM engages in several types of collecting, including:

Evidence-based

NLM supports and collects web-based collections of valuable evidence-based, well-cited reviews and guidance in biomedicine, health care and life sciences research. The Library’s collecting emphasis is on those resources that cite and provide systematic, methodological, and comparative review and commentary on current primary scientific sources and data, in order to guide further research, clinical practice, public health management, and health policy development.

Event-based

NLM collects web sites and social media that document government and non-government responses to health crises, such as major epidemics, early responders; news; perspectives of those experiencing the disaster first-hand as patients, victims or caregivers; or social and political debates surrounding the event. Content in this type of collection is crawled frequently for a specified period of time.

NLM collects web content related to events when international, federal, state, or local emergency declarations are enacted, such as the World Health Organization‘s declaration of a Public Health Emergency of International Concern (PHEIC).

Examples of event-based collecting are: "Avian Influenza A (H7N9) Virus" and "Global Health Events".

NLM uses other points of action for determining whether and for how long to collect content documenting an event, including:

• Dominance in the news media,
• Frequency of new or changing content, and
• Social media tracking.

Thematic

NLM collects web content around themes or topics of contemporary interest, including HIV/AIDS, the Opioid Epidemic, Environmental Health, and topics related to NLM exhibitions or symposia.

NLM institutional web archive

NLM periodically captures and archives large portions of its own web domain, including NLM blogs and social media, and institutional documentation.