A(n) union is a form of regional integration that includes free trade among member countries and common trade barriers with the rest of the world.

A customs union is the type of regional integration that includes free trade among member countries along with the establishment of common trade barriers with non-member countries. In a customs union, the member states eliminate tariffs and quotas on goods and services traded among themselves, allowing for an unrestricted flow of trade. Simultaneously, they adopt a unified external trade policy by imposing the same tariffs and trade regulations on imported goods from outside the union. This arrangement aims to enhance economic cooperation, boost trade, and create a more competitive market environment among member nations. Examples of customs unions include the European Union (EU) in its earlier form and the Southern African Customs Union (SACU). Implementing a customs union can lead to economic growth by increasing market access, attracting investment, and promoting efficiency among member states. However, it may also come with challenges such as the need for coordinated economic policies and adjustments to protect member industries.