Like its predecessor, The Dynasty of Chernigov 1054–1146, this book is based on an examination of primary sources. From among these, the chronicles of Rus′ have once again served as the main reservoir of information. Nevertheless, they cannot be taken at face value. We must keep in mind that not one chronicle copy from the twelfth or the thirteenth century has survived. Chronicles written at the courts of the princes under investigation were incorporated into later compilations and have come down to us, for the most part, in those from the fifteenth and the sixteenth centuries. Consequently, in evaluating chronicle accounts, we must keep in mind the biases of the original chronicler and of later compilers. Moreover, errors crept into the texts during the course of recopying when scribes inadvertently made mistakes through ignorance, carelessness, or fatigue. In some instances compilers changed the text when they sought to improve the original in the light of their own world-view.

The dating also produces special difficulties. The chroniclers use two systems of dating: the March (martovskiy) Year and the Ultra-March (ul′tramartovskiy) Year. Both years begin with March. When the chronicle uses the March Year, the correct January year of the Christian or Common Era is obtained by taking the chronicle date, for example 6732, the date from the creation of the world according to the Byzantine calendar, and subtracting 5508, the year before Christ in which, according to Byzantine reckoning, the world was created. This gives us the January year 1224 ce.