Azure AD is a highly-available and highly-scalable identity management service for small and large organizations. It enables organizations to use their corporate credentials to authenticate to new or existing applications, factoring out the authentication process and eliminating the need for many different identities. Organizations that already use on-premise Active Directory can synchronize their identities with Azure AD to provide seamless integration between on-premises and cloud resources.
As it is your organisation’s cloud directory, you decide who your users are, what information to keep in the cloud, which can use the information or manage it and what applications or services are allowed to access that information. Application developers can integrate their applications with Azure AD to provide single sign-on functionality for their users. This enables enterprise applications to be hosted in the cloud and to easily authenticate users with corporate credentials. It also enables SaaS providers to provide easier authentication for users in Azure AD organizations when authenticating to their services.