On the Government of Rulers, a book that influenced much of the political thought of the later Middle Ages, the Renaissance, and the Early Modern period, is here translated into English in its entirety for the first time. Completing a work that has long been attributed to Thomas Aquinas, Ptolemy of Lucca finished On the Government of Rulers around the year 1300. More than any other figure of his age, Ptolemy combined the principles of Northern Italian republicanism with Aristotelian theory. He was the first medieval political theorist to attack kingship as despotism. Ptolemy was the fist to draw parallels between ancient Greek models of mixed constitution and the Roman Republic, biblical rule, the Church, and medieval government. Again anticipating the Humanists, he was the first to suggest that the perfect republic might be so harmonious that it would transcend the normal imperatives of decay and ultimate destruction. On the Government of Rulers is also unique among scholastic works for its wealth of vivid examples and anecdotes on topics ranging from the minting of money, to the procedure for taking secret ballots, to the hunting habits of the French and English kings. Fluidly translated and superbly annotated by James Blythe, this long-neglected book is now made accessible to specialist and non-specialist alike.