These are the two volumes containing papers and commentaries presented at the Eleventh World Congress of the Econometric Society, held in Montreal, Canada in August 2015. The papers provide state-of-the-art guides to the most important recent research in economics. Written by the leading specialists in their fields, these volumes include surveys and interpretations of key developments in economics and econometrics, and discussion of future directions for a wide variety of topics, covering both theory and application. The first volume includes theoretical and applied papers addressing topics such as dynamic mechanism design, agency problems, and networks. The second volume addresses topics such as big data, macroeconomics, financial markets, and partially identified models.