Azure AD provides you with a common identity and access capabilities to all web services.
Whether you are using Microsoft Azure, Office 365, or others, you're already using Azure AD to help turn on sign-on and access management for all these services.
All users who are set up to use web services are defined as user accounts in one or more Azure AD instances. You can set up these accounts for free Azure AD capabilities like cloud application access.
Azure AD paid services like Enterprise Mobility + Security complement other web services like Office 365 and Microsoft Azure with comprehensive enterprise-scale management and security solutions.