What is Azure Active Directory (Azure AD / Entra ID)?

Azure Active Directory (now called Microsoft Entra ID) is Microsoft's cloud-based identity and access management service.

**Key features:**
- **Single Sign-On (SSO)** — one login for Microsoft 365, Azure, and thousands of SaaS apps
- **Multi-Factor Authentication (MFA)** — extra security layer
- **Conditional Access** — block access from untrusted locations/devices
- **B2B collaboration** — invite external users to your tenant
- **B2C** — customer identity management for your apps

**Difference from on-premises AD:**
- Azure AD is cloud-based and REST/OAuth/SAML based
- Traditional AD is LDAP/Kerberos based for on-premises

Almost every enterprise using Microsoft products uses Azure AD for authentication.