The Spanish Civil War (1936-1939) is still today subjected to heated discussions and public debates. As with the Vietnam War 30 years later, the civil war in Spain had a deep impact outside the area in which the military battle took place. Thousands of books have since contributed to the understanding of what started as an internal Spanish clash, but ended in an international conflict. Nazi Germany and Fascist Italy's support to General Franco's military rebellion as well as Soviet Union's defence of the Republic, provided the civil war with an ideological dimension which has left its imprint on the historical interpretations ever since. However, in spite of huge scientific and public interest in the civil war, our knowledge of this crucial event is not as complete, as one might assume. Actually, it is only in recent years that we have acquired a more precise knowledge of the way the great powers handled the conflict. This is due essentially to the fall of the Berlin Wall in 1989, which led to the sudden release of a wide range of important documents from archives across the world. Inspired by these new insights, the different chapters of the present study, written by some of the foremost researchers in the field, offer an original interpretation and reveal little-known or hitherto neglected aspects of one of the most controversial conflicts of the 20th century.