John Stuart Mill's philosophy contains an important 'radical' dimension, deriving from his early exposure to the philosophies of Jeremy Bentham and of his father, James Mill. In this chapter, I argue that the doctrine Mill termed 'philosophic radicalism' is best understood as an attempt to initiate political reform by introducing radically democratic institutions, avoiding narrowly 'sectarian' assumptions about utility and social theory. Contrasting Mill's understanding of philosophic radicalism with Bentham's early and late democratic theory, I show that philosophic radicalism characterized by its critique of 'aristocratic' privilege and the corresponding aim to uproot it, but also by commitments of varying intensity to the extension of the franchise, to public and parliamentary deliberation, and to the 'omnicompetence' of democratic legislation.