This thesis charts the development of the political and diplomatic relations between England and the Holy Roman, Medieval or German Empire during the reign of Henry III of England, 1216-1272. This will be done before the wider background of contemporary European politics. Therefore, relations between the two realms have been viewed in the context of events and developments such as the papal-imperial conflict, the Mongol invasions, and the crusades. The actions of either Henry III or his Imperial counterpart cannot be understood without this background in mind, and without a comparison to the actions and undertakings of their contemporaries. As a result, it emerges that Henry III's policies towards the Holy Roman Empire did not differ greatly from those of other rulers, such as Louis IX of France or Ferdinand of Castile, and that in his case, as in theirs, the immediate pressing needs of Henry's own kingdom formed and moulded the direction of his relations with the rulers of the Empire. As far as the Emperor was concerned, on the other hand, England was perceived to be a potential source of fiscal and diplomatic support, but was not considered worth any risks. At the same time, the dangers and challenges facing both rulers also forced them over and over again to confront each other's needs and ambitions.