Active Directory (AD) is Microsoft’s directory service for Windows networks. It stores information about users, computers, groups and policies, and provides a central place to manage sign-in, access to resources, and device configuration. The core component is Active Directory Domain Services (AD DS), which runs on domain controllers. AD relies on DNS for name lookups and service location, and it supports standard protocols such as LDAP for directory queries and Kerberos for authentication. AD is organised into domains, which can be grouped into trees and forests. Within a domain, organisational units (OUs) let you group objects and delegate administration. Group Policy applies settings to users and computers at scale, while replication keeps domain controllers in step with each other. Trust relationships allow users in one domain or forest to access resources in another. Administrators typically work with tools such as Active Directory Users and Computers, the Active Directory Administrative Centre, and PowerShell modules. Many organisations also use Microsoft Entra ID, previously called Azure AD, alongside AD for cloud-based identity and apps, often with synchronisation between the two.
