This Archival Research Guide (ARG) aims to provide the user with a broad overview of the Archival Directory, a key component of the CENDARI Virtual Research Environment. The CENDARI Archival Directory consists of all available data in the AtoM application (“Access to Memory”) and data in the main repository, which is derived from international or national aggregators as well as national archives or other data providers. All data, whether manually inputted via the AtoM application or collected from institutions, form together the Archival Directory. In this guide the term “Archival Directory” refers only to the application AtoM and it hence will be used in this narrow sense. The term “Archival Directory AtoM” reinforces this definition. Unlike most of the other ARGs in CENDARI, this is not a thematic overview of a historical subject but instead a practical guide to the Archival Directory AtoM’s aims and how it was created and organised. This guide will present the methodology used by researchers associated with the CENDARI project when creating archival description and archival institution entries in CENDARI. It explains how material was selected to be entered into the Archival Directory AtoM, which institutions were considered as ‘hidden archives’ by the CENDARI team, what material was not included, the limitations of the project and the future of the Archival Directory AtoM. The CENDARI Archival Directory AtoM can be accessed both directly from the website and indirectly via the link provided in the Note-Taking Environment (NTE).