Economists generally agree that trade barriers are detrimental and decrease overall economic efficiency, this can be explained by the theory of comparative advantage. In theory, free trade involves the removal of all such barriers, except perhaps those considered necessary for health or national security. In practice, however, even those countries promoting free trade heavily subsidise certain industries, such as agriculture and steel. Examples of free trade areas are: North American Free Trade Agreement (NAFTA), South Asia Free Trade Agreement (SAFTA), European Free Trade Association, European Union (EU), Union of South American Nations. Other trade barriers include differences in culture, customs, traditions, laws, language and currency. This new book is based on information from The Office of the United States Trade Representative (USTR).