This year's Nobel Prize in Economics celebrates two contributions that underlie contemporary understanding of the economics of innovation, and consequently, of economic growth. One, by Joel Mokyr, has already been featured in an article in the ARA (by Albert Carreras, October 13). I will dedicate this one to the work of Philippe Aghion and Peter Howitt, who jointly formulated a theory of innovation based on Joseph Schumpeter's concept of "creative destruction." It is rigorous, empirically testable, and useful for public policy.