The Introduction gives a brief account of Bartolus’s life, explains the world of medieval law in which he worked, and then explains the political context of the northern and central Italian city republics for which he worked, and whose problems he sought to analyse. It explains that tyranny was Bartolus’s main preoccupation, even in the two treatises ostensibly concerned with other questions. It then presents the main arguments of his three political treatises and Bartolus’s main political theory in his academic legal commentaries, and describes the later influence of these treatises in European political theory. The Introduction also argues that Bartolus conceived of these three treatises as one composite treatment of tyranny.

Bartolus of Sassoferrato, the leading jurist of his day, whose influence spanned several centuries, first formulated an equation of family and its property (substantia) that cast an image of family enduring over time in the immediate passage of property from father to son. That tie was so pivotal that a son could be termed, however incorrectly in strict legal terms, as a co-owner of the estate with his father. Disinheritance was difficult to conceive of in these terms, although it was an allowed legal institution. Subsequent jurists followed Bartolus's lead, even though they were likely to face only situations where the paradigmatic passage of haereditas from father to son was not possible.