International economics is concerned with the effects upon economic activity from international differences in productive resources and consumer preferences and the international institutions that affect them. It seeks to explain the patterns and consequences of transactions and interactions between the inhabitants of different countries, including trade, investment and transaction.

• International trade studies goods-and-services flows across international boundaries from supply-and-demand factors, economic integration, international factor movements, and policy variables such as tariff rates and trade quotas.
• International finance studies the flow of capital across international financial markets, and the effects of these movements on exchange rates.
• International monetary economics and international macroeconomics study flows of money across countries and the resulting effects on their economies as a whole.
• International political economy, a sub-category of international relations, studies issues and impacts from for example international conflicts, international negotiations, and international sanctions; national security and economic nationalism; and international agreements and observance.

The economic theory of international trade differs from the remainder of economic theory mainly because of the comparatively limited international mobility of the capital and labour.^[5] In that respect, it would appear to differ in degree rather than in principle from the trade between remote regions in one country. Thus the methodology of international trade economics differs little from that of the remainder of economics. However, the direction of academic research on the subject has been influenced by the fact that governments have often sought to impose restrictions upon international trade, and the motive for the development of trade theory has often been a wish to determine the consequences of such restrictions.

The branch of trade theory which is conventionally categorized as “classical” consists mainly of the application of deductive logic, originating with Ricardo’s Theory of Comparative Advantage and developing into a range of theorems that depend for their practical value upon the realism of their postulates. “Modern” trade analysis, on the other hand, depends mainly upon empirical analysis.