Active Diroctory Active Directory (AD) is a directory service  created by Microsoft  for Windows domain windows server   operating systems. Active Directory provides a central location for network administration and security. Server computers that run Active Directory are called domain controller. An AD domain controller   authenticates and authorizes all users and computers in a Windows domain type network assigning and enforcing security policies for all computers and installing or updating software. For example, when a user logs into a computer that is part of a Windows domain, Active Directory checks the submitted password and determines whether the user is a system administrator or normal user.