William Brian Arthur (born 31 July 1945) is an economist credited with developing the modern approach to increasing returns. He has lived and worked in Northern California for many years. He is an authority on economics in relation to complexity theory, technology and financial markets. He has been on the external faculty at the Santa Fe Institute, and a Visiting Researcher at the Intelligent Systems Lab at PARC. He is credited with the invention of the El Farol Bar problem.