Duckworth's work is supported by a grant from the John Templeton Foundation. Heckman's work is supported by NIH R01-HD043411, and grants from the American Bar Foundation, The Pew Charitable Trusts, and the Partnership for America's Economic Success, and the J.B. Pritzker Consortium on Early Childhood Development. Ter Weel's work was supported by a research grant of the Netherlands Organisation for Scientific Research (grant 014-43-711). Chris Hsee gave us very useful advice at an early stage. We are grateful to Arianna Zanolini for helpful comments and research assistance. We have received very helpful comments on various versions of this draft from Gary Becker, Dan Benjamin, Dan Black, Ken Bollen, Sam Bowles, Frances Campbell, Flavio Cunha, John Dagsvik, Michael Daly, Kevin Denny, Liam Delany, Thomas Dohmen, Greg Duncan, Armin Falk, James Flynn, Linda Gottfredson, Lars Hansen, Joop Hartog, Moshe Hoffman, Bob Hogan, Nathan Kuncel, John List, Lena Malofeeva, Kenneth McKenzie, Kevin Murphy, Frank Norman, David Olds, Friedhelm Pfeiffer, Bernard Van Praag, Elizabeth Pungello, Howard Rachlin, C. Cybele Raver, Bill Revelle, Brent Roberts, Carol Ryff, Larry Schweinhart, Jesse Shapiro, Rebecca Shiner, Burt Singer, Richard Suzman, Harald Uhlig, Sergio Urzua, Gert Wagner, Herb Walberg, and participants in workshops at the University of Chicago (Applications Workshop), Iowa State University, Brown University, University College Dublin, and Washington State University. The views expressed in this paper are those of the authors and not necessarily of the funders or commenters listed here. A website, http://jenni.uchicago.edu/econ-psych-traits/, presents supplemental tables. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research.