The Allied Masonic Degrees are an invitational organization, and requires membership in the Royal Arch as well as the Symbolic Lodge. Membership is limited to 27 members per council.  

The Allied Masonic Degrees are detached degrees some of which, many years ago, were conferred under Craft warrants and formed part of the then loosely governed Freemasonry of the period.

The Grand Council of Allied Masonic Degrees
the United States of America