Swedish economist who gained international prominence through his work on world monetary problems at the Brussels Conference in 1920 and on the League of Nations Finance Committee in 1921.

Cassel was educated at the University of Uppsala and Stockholm University and served as a professor of economics at the latter (1904–33). His most important contribution was his concept of purchasing power parity. For example, if a barrel of oil sells for $25 in the United States and if one dollar buys 105 yen, then a barrel of oil should sell for 2,625 yen in Japan (25 × 105). In short, there should be parity between the purchasing power of dollars in the United States and their exchange value in Japan.

Cassel believed that, if an exchange rate was not at parity, it was in disequilibrium—either prices or the exchange rate would adjust until parity was again achieved. Parity would be ensured by arbitrage, a type of trade that is based on price differentials between international markets. Arbitrageurs typically buy low and sell high until the difference in prices is eliminated. Cassel's view is, strictly speaking, incorrect, because not all goods are internationally traded. Nevertheless, it is a useful starting point, especially when the rate of inflation is considered. If one country maintains a higher inflation rate than another, then purchasing power parity predicts that the country with the higher inflation rate will lose value relative to the other country's money.

In 1933 Cassel was sent by the Swedish government to the World Economic Conference in London. He also represented Sweden at several meetings of the International Chamber of Commerce.