 Dave Cass's first major contribution to economics was the characterization of optimal growth trajectories in his thesis work under Hirofumi Uzawa’s supervision at Stanford University.The celebrated Cass criterion for optimal time paths in the one good growth model quickly followed.The essence of this work is the search for price characterizations of efficiency for dynamic time paths, an effort that directly pointed the way to the subsequent full dynamic decentralization of the neoclassical optimal growth model, a fact that permits its use for modeling a wide range of business cycle and other macroeconomic phenomena.