internal static void GetDomain()
{
	var context = new DirectoryContext(DirectoryContextType.Domain);
	var domain = Domain.GetDomain(context);
	Console.WriteLine("Full domain:");
	Console.WriteLine(domain.Name); //takana.local
	Console.WriteLine();
	Console.WriteLine("root container");
	var parts = domain.Name.Split(new\[\] {"."}, StringSplitOptions.RemoveEmptyEntries);
	var dcParts = parts.Select(n => "dc=" + n).ToArray();
	var d = string.Join(",", dcParts); //dc=takana, dc=local
	Console.WriteLine(d);
}

groupName = "an\_ad\_group";
PrincipalContext ctx = new PrincipalContext(ContextType.Domain);
GroupPrincipal grp = GroupPrincipal.FindByIdentity(ctx, IdentityType.Name, groupName);
var principals = grp.GetMembers(true);
```But what about an OU? There is no OrganizationUnitPrincipal... [Well, there is a solution: to instantiate a context for your OU](http://stackoverflow.com/a/1927476/632117 "See the solution on Stack Overflow"): So if you want to check if a user in a OU:

public static string GetDistinguishedName(string login)
{
   var dn = "";
   UserProfile up;
   using (var site = new SPSite("http://dev"))
   {
      var serviceContext = SPServiceContext.GetContext(site);
      var upm = new UserProfileManager(serviceContext);
      var exists = upm.UserExists(login);
      if (!exists)
         upm.CreateUserProfile(login);
      if (exists)
      {
         up = upm.GetUserProfile(login);
         dn = up\[PropertyConstants.DistinguishedName\].Value.ToString();
      }
   }
   return dn;
}
```The code is simplified and doesn't contain any error handling. And a better handling of upm.UserExists must be implemented: If upm.CreateUserProfile(login) runs, it doesn't make it so quickly and the next step won't run (upm.GetUserProfile). If you are not working in SP Context, you can see the distinguished name for a user in Powershell:

//PrincipalSearcher
internal static void ListPrincipalsFromOu()
{
	using(var ctx = new PrincipalContext(ContextType.Domain, "takana.local", "OU=SOME\_OU ,DC=takana, DC=local"))
	{
		using (var up = new UserPrincipal(ctx))
		{
			using (var ps = new PrincipalSearcher(up))
			{
				using (var res = ps.FindAll())
				{
					foreach (var p in res)
					{
						Console.WriteLine(p.SamAccountName);
					}
				}
			}
		}

	}
}
//DirectorySearcher
internal static void ListAdEntriesFromOu()
{
	const string property = "sAMAccountName";
	var ldapcon = new DirectoryEntry("takana.local") {
		Path = "LDAP://OU=SOME\_OU,DC=takana,DC=local"
	};
	var search = new DirectorySearcher(ldapcon);
	search.PropertiesToLoad.Add(property);

	using (var results = search.FindAll())
	{
		foreach (System.DirectoryServices.SearchResult result in results)
		{
			using (var entry = result.GetDirectoryEntry())
			{
				if (entry.Properties\[property\].Count > 0)
				{
					Console.WriteLine(entry.Properties\[property\]\[0\]);
				}
			}
		}
	}
}