This is the third of three volumes containing edited versions of papers and commentary discussions presented at the Ninth World Congress of the Econometric Society, held in London in August 2005. The three volumes are the latest addition to the series of World Congress proceedings with the scientific prestige of the Econometric Society. The three editors of the three volumes are the co-chairs of the World Congress’ Program Committee, and the contributors are leading specialists in their fields in the world. The first volume contains papers on economic theory, broadly defined. The second volume contains papers on applied work—applied economics and applied econometrics, again broadly defined. The first volume was reviewed by Ordaz (2007) in Technometrics.