This document provides an overview of health information systems. It begins by defining a health information system as a system designed to manage healthcare data, including electronic medical records, hospital operations, and systems supporting healthcare policy decisions. It notes that health information systems commonly access, process, or maintain large volumes of sensitive data, so security is a primary concern. The document then discusses definitions of health care information systems and their components. It provides an example of how data might be recorded and where during a patient's visit. Finally, it outlines different architectures for health information systems, including stand-alone, centralized, decentralized, and federated systems.