The present study addresses the system of transatlantic relationships which, while not without difficulties and discomforts, are at the same time in a state of continual development and expansion. Starting from the historical and diplomatic antecedents and the main characterisitics of the commercial and investment relationships between the EU and the USA, the authors examine the components and operating mechanisms of bilateral economic, co-operation. In describing economic relationships, the authors attempt to answer the questions of how accurate the expression "Siamese Twins" is when applied to transtatlantic co-operation, how the bilateral relationships influence NATO and EU expansion, and what the future holds for transatlantic co-operation.