This document provides an overview of understanding and tracking Office 365 usage and adoption. It defines what constitutes an active user for various Office 365 workloads like Exchange Online, SharePoint Online, OneDrive for Business, Yammer, Skype for Business, Office, Office 365 Groups, and Microsoft Teams. It also describes the various activity reports available in the Microsoft 365 admin center to track usage of these workloads over time periods of 7-180 days. Additional tools discussed include Microsoft 365 Usage Analytics in Power BI, usage reports, and various Office 365 governance tools to manage groups and licenses.