William Arnold Barnett (born October 30, 1941) is an American economist, whose current work is in the fields of chaos, bifurcation, and nonlinear dynamics in socioeconomic contexts, econometric modeling of consumption and production, and the study of the aggregation problem and the challenges of measurement in economics.

Barnett is currently the Oswald Distinguished Professor of Macroeconomics at the University of Kansas and Director of the Center for Financial Stability, in New York City.

He is Founding President of the Society for Economic Measurement, Founding Editor of the Cambridge University Press journal, Macroeconomic Dynamics and of the Emerald Group Publishing monograph series, International Symposia in Economic Theory and Econometrics, and originator of the Divisia monetary aggregates and the "Barnett critique".

His publications on bifurcation analysis and nonlinear dynamics have shown that robustness of dynamical inferences is compromised, when policy simulations are run only at point estimates of parameters, since confidence regions about those estimates are often crossed by bifurcation boundaries.

His MIT Press book, Getting It Wrong: How Faulty Monetary Statistics Undermine the Fed, the Financial System, and the Economy, ISBN 978-0-262-51688-4, won the American Publishers Award for Professional and Scholarly Excellence (the PROSE Awards) for the best book published in economics during 2012.