Circular letters (CL) signed by the Director-General are addressed to the Governments of Member States or National Commissions for UNESCO in the course of official business. For example, they are used to inform the Governments, to solicit information from them and ask for their position on certain questions, to send invitations to conferences, to invite applications for higher posts in the Secretariat.

All official UNESCO Documents produced by the Director General of UNESCO.

The rules on what is to be considered as a Main documents have changed throughout UNESCO’s existence. According to the definition giving in the UNESCO Manual, Secretariat handbook on administrative methods and precedures, main documents are:
Main series documents are mostly programme documents of a definitive nature which are distributed to all Member States. They include i.a. reports of meetings, surveys, analysis of replies to questionnaires and bibliographical and clearing house material.

Instructions of a temporary nature, or which are subject to frequent change, are conveyed to the Secretariat by Administrative Circulars.

Depending on the area regulated and the issuing authority, there are two types of Administrative Circular:

1. Administrative Circulars on activity, finances and property
2. Administrative Circulars on personnel matters