The introduction of the euro was initially expected to boost trade by an enormous percentage. Following many downward revisions of original estimates the current consensus estimate amounts to an increase of about 5 per cent. In view of the initial high expectations this is often seen as a dismal result. It is, however, based on aggregate data and may therefore hide important microeconomic gains that arise even for a given level of trade flows. This paper uses detailed product and firm level data to shed light on these hidden gains.