This graduate thesis studies the activity of the Teutonic Knights in the area of the southeastern rim of Catholic Europe, specifically in the historical areas of today's Slovenia and the Kingdom of Hungary. The observed period includes the High and Late Middle Ages. The paper discusses the military, ecclesiastical, political, diplomatic, ethnic and economic aspects of the Teutonic Knights with regard to the reigns of Andrew II. of the House of Árpád and Sigismund of Luxembourg, who invited them to their countries due to reasons of defense. The same aspects are discussed in the context of the Slovenian lands in the Middle Ages. This thesis attempts to answer the questions of mutual relations and mutual interests of the Teutonic Order and the Hungarian Crown. In the case of Andrew II. who invited them due to the incursion of the pagan Cumans, a conflict with the Knights occurred, that was at the same time closely connected with the Holy See. As for Sigismund of Luxembourg, the work is mostly focused on how the defense of the Banate of Severin was organized in the context of the threat to the kingdom's borders caused by the Ottomans. In contrast to the Kingdom of Hungary, in Slovenian historical areas the order particularly distinguished itself by the establishment of numerous commanderies and dynamic church and economic activities. The thesis also indicates how the order's presence was reflected in two bordering historical regions with the aim of comparing its activities and noticing their similarities and differences.