世界貿易組織的多邊貿易規則，明確承認發展中國家尤其是最不發達國家的特殊利益和要求，在實施期限和義務水平上，都對發展中國家尤其是最不發達國家作出了特殊的安排。
一、特殊差別待遇與普遍優惠待遇的確立
1947年成立初期的GATT的23個締約方中，有11個發展中國家。但是1947年總協定最初並沒有關於發展中國家的特殊規定。1955年關貿總協定作了第一次重要的修訂，可看作是特殊和差別待遇的起源。這就是第18條關於發展中國家的特殊規定。GATT第18條題為政府對經濟發展的援助，中心思想是發展中國家有更多的自由使用數量限製及其他限製措施保護其幼稚工業和國際收支平衡。具體內容是：
（1）關稅再談判，第18條A節規定，經濟上處於發展初期階段的締約方（現為WTO成員）為加速某一特定工業建立以提高人民生活水平，可以較為靈活地修改或撤銷關稅減讓表中的某些減讓，但需通知締約方全體（現應為貨物貿易理事會）成員，並與有利害關係的其他成員談判。如達成協議，受損失的成員有權對采取措施的成員實行對等減讓。
Section A：7.（a）If a contracting party coming within the scope of paragraph 4 （a） of this Article considers it desirable, in order to promote the establishment of a particular industry* with a view to raising the general standard of living of its people, to modify or withdraw a concession included in the appropriate Schedule annexed to this Agreement, it shall notify the CONTRACTING PARTIES to this effect and enter into negotiations with any contracting party with which such concession was initially negotiated, and with any other contracting party determined by the CONTRACTING PARTIES to have a substantial interest therein. If agreement is reached between such contracting parties concerned, they shall be free to modify or withdraw concessions under the appropriate Schedules to this Agreement in order to give effect to such agreement, including any compensatory adjustments involved.