The question of a United States of Europe has been discussed so frequently by journalists and political agitators that it is a great relief to have a detailed presentation of the subject by an experienced statesman. As the readers of FOREIGN AFFAIRS will remember, ex-Premier Herriot strongly believes it not only desirable but necessary to set up some type of union. After outlining the past history of the idea of European solidarity, he analyzes the problem as it confronts the Continent at the present time. The approach is from the economic angle, with reference especially to the question of tariffs, cartels, international finance and labor. These factors, M. Herriot believes, impose the union upon the states of Europe. But the union, to be successful, must be within the framework of the League of Nations. It must, furthermore, respect national institutions, must be open to all states which wish to join, including England, in spite of her extra-European interests, and must give all members a position of absolute equality. The form might be modelled upon the Pan-American Union, at any rate it must be flexible and not over-ambitious. The primary purpose should be industrial concentration and the protection of the European market. The abolition of tariff barriers should be considered as the end rather than the beginning of economic organization. Finally, in order to assure stability, the union should be accompanied by a system of arbitration, disarmament and security. M. Herriot's little book is beautifully written and very stimulating.