This selection of over 100 texts, nearly all appearing for the first time in English translation, illustrates the struggle between the Christians and Ottomans on the Danube frontier, and features coverage of the broader political, military, and diplomatic debates provoked in Christendom by the spectre of the Turkish threat in the Balkans. Sigismund of Luxemburg, as King of Hungary and Holy Roman Emperor, was at the forefront in crafting the response to the Ottomans in the first few decades of the fifteenth century. He personally led military campaigns on the Danube frontier and was instrumental in bringing the political elites of Europe together to discuss programmes which could defend Christendom, notably at the ecclesiastical assemblies of Constance (1414-1418) and Basle (1431-39), as well as at political assemblies such as the Congress of Lutszk (1429) and the Nuremberg Reichstag (1431). The range of materials in this volume, including items of correspondence, financial accounts, orations, synodal documents, and military memoranda, many of which have never been published before, shed light on the varied manners in which he sought to combat Ottoman expansion, and places his efforts within the broader context of Christendom'e(tm)s response to the Turkish threat. The texts chosen do not just shed new light on the military responses of the so-called 'e~frontline'e(tm) Catholic powers, such as Hungary, Poland and Austria, but highlight hitherto largely unnoticed diplomatic and political methods utilised to combat the Turkish threat in the early decades of the fifteenth century, including the use of public ceremony, the manipulation of crusading propaganda and motifs, and the employment of chivalric orders. In spite of the Christian reversals in the Balkans and the often terrifying spectre of the Ottoman advance in contemporary imaginations, these texts reveal the continuing energy, innovation and purpose throughout Christendom which accompanied the efforts to resist the Turks.