This Special Issue marks the 100th anniversary of the first publication of two major books by economists on and around the themes of probability, risk and uncertainty: Frank Hyneman Knight’s Risk, Uncertainty, and Profit and John Maynard Keynes’ A Treatise on Probability. Knight’s book was written for economists, went on to become a classic within the discipline, and continues to be widely cited to this day on topics ranging from entrepreneurship to insurance design. Keynes’ book, in contrast, was written for a philosophical audience, initially ignored by economists save for a few early reviews, and subsequently overshadowed by his own magnum opus, The General Theory of Employment, Interest and Money, published in 1936. Yet the General Theory, alongside Keynes’ 1937 reply to its critics, marked something of a return to themes first explored in A Treatise on Probability and this, spurred by rising interest in expectations with the advent of the Rational Expectations Hypothesis and the New Classical Economics in the late 1970s and early 1980s, inspired a small but continuing stream of research on his earlier work by economists. Partly as a consequence of this research, Keynes’ A Treatise on Probability is now also routinely cited on the subject of uncertainty, sometimes in tandem with references to Knight, predominantly in various branches of heterodox economics, but also in more mainstream contributions to economics, decision theory and management.