Least developed countries (LDCs) are granted preferential tariff treatment in the markets of developed and developing countries under several schemes and arrangements. Since its inception, UNCTAD has assisted government in developing preferential rules of origin (RoO), starting from the RoO from the Generalized System of Preferences. UNCTAD assists Governments in negotiating and drafting RoO under preferential trade agreements as well as non-preferential rules of origin. Most recently UNCTAD's technical assistance has focused on the implementation of the WTO's 2005 Hong Kong decision on Duty-free, Quota-free market access, and understanding and drafting RoO.

UNCTAD assists the least developed countries (LDC) group of the WTO in the elaboration of proposals on RoO, and in preparations for the negotiations of the Committee on Rules of Origin (CRO). Assistance is also provided through one-on-one training sessions, the drafting of advisory memoranda, and the elaboration of background documents, briefing notes and ad hoc presentations.

In 2015, UNCTAD launched a training and research partnership with the European University Institute specifically targeted to LDCs. Executive trainings enhance the skills and knowledge of officials from LDCs, equipping them with the necessary tools to devise a negotiating strategy on preferential RoO. Several training sessions have already taken place, and more are to come.