Following the October Revolution of 1917, a revolutionary wave swept across Europe. In this period, Leon Trotsky, along with Lenin, was pivotal in setting up the Third (Communist) International, which represented a world party of the working class. The International could not be conjured out of thin air. Much like the Bolshevik Party, it had to be built through struggle against many different tendencies and ideas. This book collects all of Trotsky's writings and speeches related to the first five years of the Communist International. Highlighting the task he and Lenin faced in trying to educate the young communist parties of Germany, France and elsewhere, it deals with many problems that the working-class movement still comes up against today. This includes the question of the United Front, the national question, the consciousness of the working class and how it changes and much more. Today, the capitalist system faces the deepest crisis in its history. However, we are faced with the same problem Trotsky outlined in 1924: there is no mass international organisation of the working class with a clear understanding of the task at hand. Therefore, this work is not just of historical interest, but should be read as a guide to action for all workers and youth seeking a revolutionary way out of the present crisis. This edition contains a new introduction by Fred Weston, editor of Marxist.com, which outlines some of the key debates and decisions as well as an outline of the development of the International in this period.