Tariff and non-tariff barriers are widespread as applied to agricultural trade. The theory of gains from trade considers the impacts of free trade relative to no trade and to non-tariff barriers, while the theory of agricultural policy generally places little weight on the international trading sector. However, it is necessary to combine agricultural policy with the international trading sector so that agricultural policy instruments such as price supports are considered together with barriers to trade such as tariffs. This is possible within the context of welfare economics when considering the costs and benefits of alternative agricultural and trade policies.