In this article, I discuss the relationship between Karl Popper’s conception of critical rationalism and William Bartley’s conception of pancritical rationalism. Both Popper and Bartley tended to identify rationality with openness to criticism, but they are usually considered to be disagreeing about whether rationality is limited or comprehensive and whether or not it applies to moral attitudes. These traditional interpretations are found wanting, and I make the case that there is—and was—no genuine, substantial conflict between Popper’s critical and Bartley’s pancritical (...) rationalism. The apparent disagreement between Popper and Bartley about critical versus pancritical rationalism is nothing but a tangle of several factors, including the misconstrual of Popper’s critical rationalism by Bartley, Popper’s disagreement with Bartley’s criticism of critical rationalism, Popper’s disagreement with Bartley’s claim that his formulation is superior to Popper’s formulation of critical rationalism in The Open Society and Its Enemies, and the clash of Bartley’s ambitions with Popper’s rather cold attitude toward his cherished ideas. New (so far unpublished and not discussed) archival material—Popper’s interview and two letters to Leslie Graves dated 1992—is invoked to provide crucial evidence for this interpretation. (shrink)