In the preface to a companion volume (Essays on medieval agriculture and general problems of the medieval economy) I have explained, and apologized for, my decision to fall in with the prevailing practice and to assemble for re-publication a number of my studies not available in book form. I should like now to cite the special reasons why the studies in this volume have been grouped together and apart from my other essays. A separate collection devoted to trade and finance can of course be justified by the conventional demarcations between different aspects of economic history. But my main justification is that the topics of commercial and financial history in this collection represent my earlier and, so to speak, preliminary approaches to medieval economic history. In embarking upon the study of medieval economic history I chose as my main subject the formation of capital and the role of capital in medieval economy. The use of money in the middle ages, the function and scope of credit, the machinery of investment, and the financial technique were all constituent parts of the main subject and were intended to lead up to its main theme – that of the sources of capital formation. I embarked on this last and most important stage by trying to compute the profits of the great estate owner who in my view controlled the bulk of productive capital.