The Diocesan Archives of the Diocese of Rockville Centre serves as the repository to preserve historical materials created by its departments and parishes. This is in accordance with Canon 486, 489, and 491, as well as the Circular Letter The Pastoral Function of Church Archives published by the Pontifical Commission for the Cultural Heritage of the Church (1997).

Archival records are records that have permanent value. Some examples are: minutes, charters, reports, correspondence, policies, organization charts, directories, handbooks, financial statements, department publications, documentation of programs / events, press releases, awards, photographs, video or audiotapes, yearbooks. Their uses may be for historical, legal, fiscal, and / or administrative reasons. Canon law, state, and federal regulations provide guidance on how long documents should be kept.

The Chancellor of the Diocese and the Diocesan Archivist are responsible for the acquisition of diocesan archival materials and all aspects of their care once they are transferred. Most of the Archives holdings are acquired through the diocesan records management program. Occasionally donations are made by individuals.

The collecting interests of the Diocesan Archives are very specific: to permanently preserve the history of the Catholic community in Nassau and Suffolk counties from 1957 onwards. Therefore, the Archives does not seek materials created by an entity outside of this diocese. This applies to written documents, books and other publications, photos, artworks, multimedia materials, and artifacts.