The main focus of interest in this PhD dissertation is the Reformation historian and diplomat Johann Sleidan (1506-1556). Born in Schleiden and brought up together with Strasbourg's famous Jean Sturm, Sleidan soon entered a period of active political life with his employment at the chancellory of Cardinal Jean Du Bellay in Paris in the mid-1530s. There and later in Strasbourg his main concern was to encourage a rapprochement or possible alliance between France and the German Protestants. It was also in Paris that Sleidan discovered history as his second passion. After translating key French historians into Latin, Sleidan moved on to produce his own works of a political-historical nature. His main work, De statu religionis et reipublicae Carolo Quinto Caesare commentarii, 'Commentaries on religion and state under Emperor Charles V', published in 1555, was initially commissioned by the Schmalkaldic League as the official history of the Reformation. Despite early hostile reactions, this history was an immediate success with the buying public, published in numerous editions and by the year 1560 circulated in six different languages. Chapters one to three explore Sleidan's biography in depth. The collection and analysis of contemporary correspondence has provided the cornerstone for a new narrative of Sleidan's life in the second half of this thesis I move to a detailed study of his principal published works. Chapter four concentrates on Sleidan's main work, the Commentaries. After placing this history in the context of contemporary German history writing, I examine this work in detail, treating its genesis, character, and methodology. I examine the unexpectedly hostile reactions to the first edition and its very rapid success with purchasers. I then move on to consider the longer-term reaction to Sleidan's great work, first in Germany and then in France. I explore the controversies aroused by Sleidan's work, among both Catholics and Protestants, and in contrast, the great respect for his scholarship that also straddled the religious confessions. Sleidan provided the context through which I have been able to analyse the life of a scholar in the sixteenth century, and the works of one of the foremost historians of the new evangelical movement. His life and his works have not, until this point, been placed in a broader context. His work as a translator and historian provides an excellent example of the movement of text around the cultural communities of Europe. Sleidan played a vital part in this process by offering Latin translations of leading French historians which would later be translated into other languages, and by publishing his own works in German or Latin, which were then translated into many other vernaculars. But Sleidan was also engaged in the world of public affairs. Sleidan's position in Du Bellay's chancellery in Paris has provided a new picture of French evangelism. This contact was not given up when Sleidan moved to Strasbourg. The Franco-imperial city has been shown again as one of the cultural centres of Europe from where an intellectual and political elite operated on a cross-national and cross-confessional level. Strasbourg with its francophone scholars was also the Schmalkaldic League's gateway to France. Sleidan's connections as a diplomat linked Germany and France, and have formed the basis for a new study of those in the Franco-German world who shared Sleidan's concerns to promote peace across the religious divide.