This document discusses how Azure Active Directory (AAD) provides identity management across Office 365 services like Exchange, SharePoint, Yammer, and others. It explains that AAD is the central identity store and manages group membership. When changes are made to a group in AAD, the other Office 365 services are notified and can extend the group with their own data and functionality, like conversations in Exchange or documents in SharePoint. Even if notifications are missed, reliability is ensured through synchronization between AAD and the other service-specific data stores. This provides a loosely coupled yet reliable model for shared identity and group management across Office 365.