In 1202, Leonardo of Pisa introduced in Europe the positional system of numeration. This system was gradually adopted, with some resistance, and algorithms were either invented or borrowed from the Indians and the Arabs for the operations of multiplication and division. Some of these methods survive up to our time, others disappeared with the invention of printing. Historians of mathematics disagree among themselves about the existence of algorithms for the operations of multiplication and division in more ancient systems of numeration. I propose to discuss these questions with you.