Frank Knight's famous dissertation "Risk, Uncertainty and Profit" (1921) remains one of the most interesting reads in economics even today. In it, Knight made his famous distinction between "risk" (randomness with knowable probabilities) and "uncertainty" (randomness with unknowable probabilities), set forth the role of the entrepreneur in a distinctive theory of profit and gave one of the earliest presentations of the now-famous law of variable proportions in the theory of production. This work is a must-read for any serious student of economics.