Abstract: This is an essay prepared for a conference in honor of Justice Samuel A. Alito, Jr., March 23-24, 2022. It offers a constructive account of Justice Alito’s jurisprudence through the lens of Lon Fuller’s 1946 essay “Reason and Fiat in Case Law,” published in the Harvard Law Review. Fuller argued that the true spirit of American law was to combine reason and positive fiat in ways that would conduce to the well-being of the community, and that our law needed to recover that sensibility. The essay examines some of Justice Alito’s most famous opinions — on administrative procedure, reviewability, and free speech — and finds them highly compatible with Fuller’s vision. Justice Alito is, plausibly, our most Fullerian justice.