public PrincipalContext GetPrincipalContext() { PrincipalContext oPrincipalContext = new PrincipalContext(ContextType.Domain,"Your Domain Name"); return oPrincipalContext; } To get the single user public UserPrincipal GetUser(string userName) { PrincipalContext oPrincipalContext = GetPrincipalContext(); UserPrincipal oUserPrincipal = UserPrincipal.FindByIdentity(oPrincipalContext, userName ); return oUserPrincipal; } To get All Users public List<string> GetAllUsers() { try { List<string> users = new List<string>(); PrincipalContext oPrincipal = GetPrincipalContext(); GroupPrincipal gPrincipal = GroupPrincipal.FindByIdentity(oPrincipal, IdentityType.SamAccountName, "Domain Users"); if (gPrincipal != null)