The Homily of the Unworthy Priest Cosmas Against the Newly-Appeared Heresy of Bogomil (10th century) is a key source for the religious history of the Balkan peninsula. It is one of the earliest and richest sources for the rise of the dualistic religious movement of Bogomilism in the early Middle Ages. Written in a period of war and crisis of the Bulgarian Empire Cosmas sermon is also an important work of Eastern Christian Theology, calling for a thorough reform of clergy and monasticism.

During the subsequent centuries Cosmas’ work was copied and excerpted by Bulgarian, Serbian and Russian churchmen who were seeking inspiration in their struggle for ecclesial reform and against religious dissent of various heretical movements. In the processes of national identity construction on the Balkans during the nineteenth and twentieth centuries Cosmas’ Homily again played a remarkable role.

The present study provides the first complete translation into a western language of Begunov’s 1973 critical edition. The German translation is accompanied by an introduction and a commentary.