Though largely neglected in recent studies about the European integration process, Salvador de Madariaga was a key forerunner and contributor to the “European idea,” as well as a highly influential Spanish diplomat, writer, historian, and pacifist at different critical junctures of the twentieth century. He was nominated for the Nobel Prize in Literature and for the Nobel Peace Prize, and awarded the Charlemagne Prize in 1973. Madariaga was also a press member of the Secretariat of the League of Nations in 1921, and chief of the Disarmament Section in 1922. In 1928, he was appointed Professor of Spanish Studies at the University of Oxford and by the start of the Spanish Civil War, he had gone into exile in the UK. In 1962, Madariaga was one of the main organizers of the meeting of different anti-Francoist opposition groups in the framework of the Congress of the European Movement in Munich. As a writer, he cultivated various genres: historical and political essay, literary criticism, novel, biography, and poetry. As a precursor of “the idea of Europe,” he defended a broad and inclusive conception of which territories should be included in “Europe,” advancing that this “idea” encompassed much more than a mere geographical continent and his approach and contributions to the European integration process have been regarded as a form of “constructive Europeanism.”