In this essay, we have attempted to sketch the conception of work of a late medieval and early modern merchant who, by now sedentary, was at the head of medium-sized business systems, engaged in manufacturing, trade and complex financial transactions. We have done so in the knowledge that each trader was different and that his behaviour was influenced by personal attitudes, character and ambitions. What emerges is a picture in which merchants, capable of 'governing' themselves and their activities, especially in the Tuscan world, lived mercantile life not only as a trade, but as a way of understanding life. Almost a mission like that of the doctor who 'works while he lives'.