The effects of the Reformation in the Military Frontier on the territory of Croatia in the 16th century were weak. There was a Protestant preacher in Karlovac, the main stronghold of the Croatian Military Frontier, who took care of the few members of the Evangelical confession that were mostly officers of Austrian-German descent or were members of the German military garrisons. Bearing in mind the poor representation of confessions arising from the Reformation in the Military Frontier during the 16th and 17th centuries, the author focuses on the gradual change of this practice at the end of the 18th and during the 19th century which took place in the newly created sections of the Military Frontier, from Slavonia to Banat and Transylvania. This area, which became part of the expanded Habsburg military zone after the war with the Ottomans at the end of the 17th century, was the location of great administrative, demographic, ecclesiastical and confessional, and economic changes during the 18th century. The paper focuses on migrations and planned settlement in the Slavonia-Srijem part of the Military Frontier that was carried out in order to maintain a functional Military Frontier system. As part of the intense and numerous migrations in the Slavonia-Srijem regiment areas during the 18th and 19th centuries, the settlement of Protestant families was mainly centred around the Srijem part of the border, especially the Petrovaradin regiment. The number of Protestants in the Military Frontier during the early 19th century, as shown by Hietzinger in his book Statistik der Militärgränze (1817 – 1823), was several times smaller in comparison to the prevailing Catholic and Orthodox population. Taking into account the legal framework and provisions regulating the settlement of Protestants in the Military Frontier, and based on original archive material and the comparison with the published data, the paper presents the course of settling of Protestant families, their origin, socio-demographic characteristics, the conditions of their settlement and the attitude of the authorities and the local population towards them. The paper describes their material circumstances in the new environment, the possibilities of performing religious ceremonies, the attitude of the population of majority confessions towards them, and their civil and religious freedoms at the Slavonian border. The research for this paper is based on written historical sources from the Slavonian general command which are stored in the Croatian State Archives in Zagreb. This material includes various documents created by the general command administration of the Slavonia-Srijem Military Frontier, which acted as a kind of provincial government in this area. The fund is part of the period from 1701 to 1848 and consists of 162 boxes of documents and 126 books. The analysed material, written exclusively in German language and script, documents the immigration and certain issues from everyday lives of “non-Catholic” families settled at the Slavonian border. It consists mostly of letters from the Aulic War Council to the Slavonian general command or command of the Petrovaradin, Brod and Gradiška regiment and Šajkaš battalion, as well as the canton commands of the same names. This includes orders for the main command of the Petrovaradin regiment, tables with the list of immigrants in the Military Frontier, and plans for their accommodation. The conducted research is focused on the decisions and plans of state authorities related to the settlement of Protestant families, but also on the implementation of these plans. The research suggests that members of confessions derived from the Reformation are referred to with the general term “non-Catholic” or “non-Catholic families” (akatholische/accatholische Familien, acatholische Reichs-Colonisten) in the analysed documents. This term applied exclusively to members of confessional denominations derived from the reformation, both to evangelicals and Calvinists. Occasionally, the documents provide a more precise description of the religion as “evangelical/Augsburg confessions/religion” (evangelische/augsburgische Konfession/Glaubensbekenntnis/Religion) or “reformed/Helvetic religion” (reformirte/helvetische Religion). Since the 1840s, phrases such as “Protestant families, Protestants” (protestantische Familien, Protestanten) are used for families of reformed denominations in the sources. It is clear from analysing the material that most of the total immigration to the Croatia-Slavonia Military Frontier occurred up to the middle of the 18th century. However, this process continued after that period as well, particularly in the Slavonia frontier, which was still poorly populated in the middle of the 18th century and provided enough land for new settlers. In the period from 1776 to 1785, over 400 families arrived from the Ottoman and Venetian-Dalmatian regions, and most of them settled in the Petrovaradin regiment. The next wave of settlements occurred during the Austro-Turkish War, from 1788 to 1791, when almost 900 families relocated from Ottoman territory, most of them settling in the area of the Petrovaradin regiment (Kaser, 1997/II: 43–44). The Reformation did not spread in the Croatia-Slavonia Military Frontier and it did not have a major impact among the population; in fact, the frontiersmen of the Karlovac and Varaždin Generalate fought against the spread of Reformation in the interior countries of the Austria, and also fought in the Thirty Years’ War as part of the imperial Catholic forces. The few Protestants who had settled there received, based on the same principle as Orthodox believers, protection for their religious beliefs in the Military Frontier (Hietzinger, 1817/I: 246). Following the adoption of the Patent of Toleration of Joseph II in 1781, the attitude towards the settlement of Protestant families in the Slavonian Military Frontier also changed. Religious freedoms and the relationships among members of different confessions were regulated by various additional provisions. Thus, in 1788, a number of circular letters were published for all the Succession Countries in which the possibility of transitioning from a non-Catholic to Catholic faith is discussed, and details for terms of divorce of non-Catholics are described in cases when one of the partners converts to Catholicism, as well as the conditions for entering into a new marriage. There were two dominant directions for immigration into the Slavonic Military Frontier. The first direction was the one from the German Empire and the Central European parts of the Habsburg Monarchy to its south-eastern areas, under the supervision of the central authorities in Vienna and the military authorities in the Frontier. The reasons for emigration are typically associated with overpopulation, lack of available land, poor socioeconomic or social status (urban poor, convicts promised amnesty) and unfavourable conditions for entrepreneurial activity, especially craftsmanship. The largest number of German colonists was settled in the German-Banat borderland, i.e. in the German-Banat canton. For example, in 1790, three transports of German colonists arrived from Alsace, Lothringia, Swabia, Württemberg and Baden numbering 1921 persons, including Protestant families. Colonists from the Rhineland also settled in the German-Banat canton, as well as the Petrovaradin regiment (Vaniček, 1875/III: 65). The second migration route, which originated in Ottoman or Venetian territory, brought much more immigrants to the Slavonian Military Frontier. Taking into account only the period of the war with the Ottomans (1788–1791), 564 migrant families moved to the area of the Petrovaradin canton. Although there are no preserved personal data in the sources for all those that the state settled, the transports of immigrants from the German Empire and Hungary to Banat in the early 1790s, which were in part also directed towards Srijem and Slavonia and passed through Petrovaradin, can be analysed based on the preserved tables in the Slavonian General Command fund. Of the six preserved lists for 1790 and 1791, two tables from July1791 are particularly important sources of demographic and socioeconomic data on evangelical settlers designated for settling on the ley (praedium) near Pazova. One of the tables contains a list of 11 Protestant families, with a total of 63 members, who headed to Petrovaradin without money or material resources to settle in Srijem. Another table contains a list of 8 families, with a total of 45 members, who had some money at their disposal. Based on data from the tables, the age and sex of the immigrants, their marital status, occupation, place of origin and their property/legal situation can be analysed. All these families were Protestant, more precisely Evangelicals, except for one Calvinist family. They were originally from various places in Württemberg. The analysis of the data from the tables revealed that most of them were simple nuclear families with an average of 3.2 underage children. The average age was 38.3 years for men, and 38.1 years for women. These were mature men and women, most of whom worked in agriculture and could be expected to contribute to the maintenance of the border system in economic and military terms. The conditions under which immigrants from German countries were settled changed over time and depended on the destination and whether they were being settled on the communal state, private estates or the Military Frontier area. However, all migration waves with a destination in the Military Frontier had the same military and economic purpose: from the state’s point of view it was important to settle those immigrants who could independently survive on the lands given to them, and if necessary, join the Frontier’s military units. The constant need for fresh recruits in the regiments necessitated repeated migrations of military-capable population into the area of the Military Frontier.