The Department of the Church History traces the emergence, development, and life of the Church, as well as its various external and internal activities during the two thousand years of its history. It puts the emphasis on the influence of the Church on social, cultural, and political relations among states and peoples. It also provides an insight into the life of the Church in the inner-ecclesial area, i.e. on the development of the Church structure, liturgy, science, and art as unavoidable cultural and civilizational factors and, thus, it provides a complete image of the historical development of the Church and the historical frame within which theology ought to be understood. The history of the Church and Christianity among Croatians is especially treated within the Department and this study proceeds on the basis of historically determined and documented facts that leads to an integral understanding of the history of the Church. In other words, within the context of events in the universal Church, the historical development of the Church among Croatians is studied and this creates the complete historical frame within which one can understand and study the development of theological thought on all levels of the Church history, universal and national. The history of the Church, as a theological discipline, is in the service of developing critical historical thought and it contributes to it by engaging in research on the basis of relating events of certain historical periods that made the Church an unavoidable factor within the history of humanity.