A proposal for a European Currency Unit (Ecu) that would initially have been equal in value to a bundle of European currencies, but could not subsequently be devalued relative to any member currency. This would have made the hard Ecu at least as hard as the hardest member currency, and harder than the remainder, and would have made it, and debt denominated in it, attractive as assets both to private investors and to national authorities as a form of foreign exchange reserves. The concept of the hard Ecu was superseded by the adoption of the euro.