Microsoft Windows Azure Active Directory (Windows Azure AD) is a cloud service that provides administrators with the ability to manage end user identities and access privileges.
The service gives administrators the freedom to choose which information will stay in the cloud, who can manage or use the information, what services or applications can access the information and which end users can have access. Windows Azure AD can be integrated with on-premises Active Directory (AD). If it's integrated with AD, administrators can allow single sign-on (SSO) so end users don't have to enter passwords multiple times to access cloud applications.
Active Directory Premium, which is a paid offering of Windows Azure AD, provides additional features including user self-service password reset, group-based application access, additional security reports and a corporate branding option.