Amongst the most valuable material for the economic history of the middle ages are the recognisances of debt which are frequently to be found in great numbers in the public archives of states and municipalities. As, however, the obligations thus recorded obviously partake in many cases of the nature of legal fictions, the interpretation of them is not a task that can be lightly attempted, except in cases where they constitute such a close sequence amongst themselves as to cast light upon each other, or where they can be brought into intelligible relations with the data of the same period. Both these conditions are fortunately fulfilled in the case of a series of recognisances contained in the " Letter Books " of the City of London, and in the following essay an attempt will be made to use this material as a means of illustrating the relations existing at the end of the thirteenth and the beginning of the fourteenth centuries between the shopkeepers of London in a variety of trades and their creditors.