Digital repositories are emerging to meet the needs of scholars and researchers who rely heavily upon digital data and content in their research. Maintaining digital resources over time is necessary to permit longitudinal or time lapse studies, and to preserve researchers' ability to support, and others to evaluate, their findings. There is a need for “long-lived” collections of digital content and data. Some repositories specialize in data for particular fields or disciplines.  Others aggregate digital content on a variety of subjects.

Various assessment criteria have been created for evaluating digital repositories. These tools can help libraries, scholars, publishers, and others to judge the reliability of the repositories and digital preservation services they may choose to rely upon for support. Of the assessment tools available, the most important for CRL's community are the Trusted Repository Audit Checklist (TRAC) and ISO 16363 (also known as The Trusted Digital Repository Checklist (TDR)).

List of all the metrics pages (not necessarily in a list)

• TRAC - Trusted Repository Archiving Checklist (TRAC) contains metrics that help in judging the repository in the areas of Administration and Policy, Object Handling and Technology. It was published by CRL in 2007.
• ISO 16363, or TDR - is an ISO standard as of February of 2012. It is a revision of the TRAC Checklist. Many of the changes were structural, and it continues to address the same core areas of repository activity. TDR is a free, unofficial version published by the Consultative Committee for Space Data Systems (CCSDS) who sponsors the working groups for TDR, OAIS and other relevant digital repository standards.
• Ten Principles - A list of ten core principles digital repositories must exhibit in order to be trusted.
• Other tools  - CRL provides access to other tools for evaluating digital repositories.