Active Directory (AD) and Azure AD (Azure Active Directory) are both directory services developed by Microsoft, but they serve different purposes and have some key differences:

1. On-Premises vs. Cloud-Based: Active Directory is an on-premises directory service that is installed and managed within an organization’s own network infrastructure. Azure AD, on the other hand, is a cloud-based directory service provided by Microsoft as part of the Azure cloud platform.

2. Authentication and Authorization: Active Directory primarily focuses on user authentication and authorization within an organization’s on-premises network. It provides features such as user and group management, single sign-on, and group policy management. Azure AD extends these capabilities to the cloud, allowing users to authenticate and access resources across cloud-based applications and services.

3. Integration with Cloud Services: Azure AD is tightly integrated with various Microsoft cloud services, such as Office 365, Azure, and other SaaS applications. It provides seamless single sign-on and user management across these services. Active Directory, being on-premises, does not have the same level of integration with cloud services.

4. Identity Management for Hybrid Environments: Azure AD supports hybrid identity scenarios, allowing organizations to integrate their on-premises Active Directory with Azure AD. This enables users to have a single identity across both on-premises and cloud resources, providing a unified identity management solution.

5. Scalability and Maintenance: Azure AD is a fully managed service provided by Microsoft, which means that Microsoft handles the infrastructure, scalability, and maintenance of the service. Active Directory, being on-premises, requires organizations to manage and maintain their own infrastructure.

In summary, Active Directory is an on-premises directory service primarily focused on user authentication and authorization within an organization’s network. Azure AD is a cloud-based directory service that extends these capabilities to the cloud, providing identity management and access control for cloud-based applications and services. Azure AD also offers integration with various Microsoft cloud services and supports hybrid identity scenarios.