Why are Europe and America still allied? After all, many observers predicted after the Cold War that NATO might collapse, trade disputes could escalate, and political relations would suffer in the absence of a common threat (like the one formerly posed by the former Soviet Union). Peter Barschdorff argues that an acquis atlantique is holding the two sides together. Common experiences, legal stock and understandings make decision-makers converge their views on controversial issues, such as peace-making in the Balkans, NATO reform and trade of agricultural goods. The acquis might change over time. But as an analytic concept and as a driver of transatlantic politics it will remain an important constant.