The use of trade policy instruments to support the achievement of environmental protection objectives goes back at least to 1973 when the Convention on International Trade in Endangered Species (CITES) was concluded. From its use of non-automatic licensing systems to control trade of certain species covered by that agreement, to outright bans on the trade of certain products as found in the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol), countries have often agreed to use specific trade policy measures or instruments as a means to implement the goals of multilateral environmental agreements. Moreover, while those measures may often run counter to the trade obligations agreed to in other international agreements, countries accept these specific conflicts between competing treaties as the trade policy measures have been identified as necessary for the implementation and achievement of the objectives of these multilateral environmental agreements.