This is DDI version 3.1, published on 2009-10-18 as approved for publication by the DDI Alliance Expert Committee, with minor revisions. The current publication includes Part I - Overview, Part II - User Guide, and Part IV - XML Schema. Part III - Model will be added as part of a minor revision. The development of DDI 3 draws on earlier DDI versions and work of the committees and individuals who developed them as well as the collective ideas, needs, and work of the Expert Committee of the DDI Alliance. Major contributions to the development and structuring of DDI 3 were made by the following individuals: Technical Implementation Committee - TIC (former Structural Reform Group - SRG): Leadership Arofan Gregory, Lead technical expert Jostein Ryssevik, Open Data Foundation, Chair [2004-2005], Vice Chair [2006] Wendy Thomas, Minnesota Population Center, Chair [2006-2009], Vice Chair [2004-2005] Joachim Wackerow, GESIS -- Leibniz Institute for the Social Sciences, Vice Chair [2007-2009] Members and invited experts: Cavan Capps, Invited expert Mark Diggory, Harvard-MIT Data Center J Gager, Technical expert Daniel Gillman, Invited standards expert Pascal Heus, World Bank, Development Data Group (DECDG) I-Lin Kuo, Invited expert Ken Miller, UK Data Archive Chris Nelson, Technical expert Oliver Watteler, GESIS -- Leibniz Institute for the Social Sciences Substantive working group members: Iris Alfredsson, Swedish Social Science Data Service (SSD) Atle Alvheim, Norwegian Social Science Data Service (NSD) Titto Assina, UK Data Archive Phil Bardsley, University of North Carolina Sandra Cannon, Invited expert Gina-Qian Cheung, Institute for Social Research, University of Michigan Karl Dinkelmann, Institute for Social Research, University of Michigan Pat Doyle, U.S. Census Bureau Ilona Einowski, University of California, Berkeley - UCDATA Janet Eisenhower-Smith, University of Wisconsin Fred Gey, University of California, Berkeley - UCDATA Peter Granda, ICPSR Ann Green, Invited expert Lon Hofmann, Invited expert Sanda Ionescu, ICPSR Jeremy Iverson, Invited expert Reto Hadorn, Swiss Data Archive for the Social Sciences (SIDOS) Taina Jaaskelainen, Finnish Data Archive Peter Joftis, ICPSR Chryssa Kappi, Invited expert Mari Kleemola, Finnish Social Science Data Archive Hans Joergen Marker, Danish Data Archive Mark G. Maynard, Roper Center, University of Connecticut Katherine McNeill-Harman, MIT Pam Miller, UK Data Archive Meinhard Moschner, GESIS -- Leibniz Institute for the Social Sciences Ron Nakao, Stanford University Tom Piazza, University of California, Berkeley - Computer-Assisted Survey Methods Program Pilar Rey del Castillo, Centro De Investigaciones Sociologicas (CIS), Spain Ed Ross, Invited expert Dan Smith, Invited expert Ed van Duizen, University of North Carolina Mary Vardigan, ICPSR We would like to thank the following member organizations which have supported the DDI Alliance in their development of DDI version 3.0: Australian Social Science Data Archive (ASSDA) University of Alberta, Canada University of California, Berkeley -- Computer-Assisted Survey Methods Program and UCDATA, USA University of California, California Digital Library, USA University of California, San Diego, USA Centro De Investigaciones Sociologicas (CIS), Spain CEPS/INSTEAD, Luxembourg Cornell University (CISER) Danish Data Archive Data Archiving and Networked Services (DANS), The Netherlands Emory University, USA Finnish Social Science Data Archive German Socio-Economic Panel Study (SOEP) GESIS -- Leibniz Institute for the Social Sciences University of Guelph, Canada Harvard University, USA Institute for the Study of Labor (IZA), Germany International Association of Social Science Information Service and Technology (IASSIST) International Federation of Data Organizations (IFDO) Inter-university Consortium for Political and Social Research (ICPSR), USA Massachusetts Institute of Technology (MIT), USA Minnesota Population Center (MPC), USA National Opinion Research Center (NORC), USA Nesstar LTD., UK University of North Carolina, USA Norwegian Social Science Data Service (NSD) Open Data Foundation, USA Pennsylvania State University, Social Science Research Institute, USA Princeton University, USA Roper Center, USA SPSS Inc., USA Stanford University, USA University of Surrey, UK Survey Research Operations, University of Michigan Swedish Social Science Data Service (SSD) Swiss Data Archive for the Social Sciences (SIDOS) University of Toronto United Kingdom Data Archive United States Census Bureau Washington State University, USA University of Wisconsin, USA World Bank, Development Data Group (DECDG) Yale University, USA DDI 3.1 XML Schema is released under the terms of the GNU Lesser General Public License. Details see the file license.txt.