A few years ago there would have been little point in writing a history of the Communist International. As recently as 1933 there was not a single country outside Russia where the communists counted as a political force. But since 1934 the Communist International has evolved a new policy, has claimed to defend democracy, has sought alliances of the closest kind with the democratic parties of various countries, and has, during this latest period, increased very considerably in strength. Today it is again important to know the Communist International. This conclusion was forced on me with particular strength when, during my field-study of the political and social problems of the Spanish civil war, I realized how important a force the Communist International had once more become.