As prime minister and finance minister of Luxembourg over 30 years, Pierre Werner played a major role in the building of a united Europe. This Christian Democratic intellectual and committed federalist gained strong reputation as a consensus-builder between larger powers (Germany and France) and between diametrically opposed positions (‘economists’ and ‘monetarists’), as well as for his ideas on monetary integration. From early 1950s, Werner advocates a European monetary system based on a currency unit and on a clearing house for central banks. In 1968 he delivered a clear roadmap to EMU founded on a symmetrical economic and monetary union, with political union as the ultimate goal. Werner’s vital input and the ‘effective parallelism’ principle he imagined, were evident in the Werner Report of 1970, which was offered as the blueprint for EMU in the EU. Based on the Werner family archives and original interviews, this chapter highlights Werner’s contribution as architect of EMU in a threefold way: intellectual input, negotiation methods and consensus building.