This document provides an overview of the HathiTrust Research Center (HTRC) architecture. It describes the key components including a portal for access, an agent for application submission, a registry for storing metadata, a secure API for programmatic access, and storage of data in a Cassandra cluster with indexing in Solr. It also outlines use cases and discusses how the architecture enables secure, non-consumptive research on copyrighted works stored in the HathiTrust digital library.