TIMSS measures trends in mathematics and science achievement at the fourth and eighth grades in participating countries around the world, while also monitoring curricular implementation and identifying promising instructional practices. Conducted on a regular 4-year cycle, TIMSS has assessed mathematics and science in 1995, 1999, 2003, 2007, and 2011. TIMSS collects a rich array of background information to provide comparative perspectives on trends in mathematics and science achievement in the context of different educational systems, school organizational approaches, and instructional practices. To support and promote secondary analyses aimed at improving mathematics and science education at the fourth and eighth grades, the TIMSS 2011 International Database makes available to researchers, analysts, and other users the data collected and processed by the TIMSS project. This database comprises student achievement data as well as student, home, teacher, school, and curricular background data for 63 countries and 14 benchmarking participants. Across both grades, the database includes data from 608,641 students, 49,429 teachers, 19,612 school principals, and the National Research Coordinators of each country. TIMSS 2011 was an ambitious and demanding study, involving complex procedures for drawing student samples, assessing students' achievement, analyzing the data, and reporting the results. In order to work effectively with the TIMSS data, it is necessary to have an understanding of the characteristics of the study, which are described fully in "Methods and Procedures in TIMSS and PIRLS 2011" (Martin & Mullis, 2012). It is intended, therefore, that this User Guide be used in conjunction with the "Methods and Procedures" documentation. Whereas the User Guide describes the organization and content of the database, the Methods and Procedures documentation provides the rationale for the techniques used and for the variables created in the process of data collection and compilation. This User Guide describes the content and format of the data in the TIMSS 2011 International Database. In addition to the Chapter 1 introduction, the User Guide includes the following three chapters: Chapter 2--This chapter introduces the IEA International Database (IDB) Analyzer software (IEA, 2012) and presents examples of analyses with the TIMSS 2011 data using this software in conjunction with SPSS (IBM Corporation, 2012). Chapter 3--This chapter presents examples of analyses with the PIRLS 2011 data using the SAS statistical software system (SAS Institute, 2011) and the SAS programs and macros included with the database. Chapter 4--This chapter describes the structure and content of the database. The User Guide is accompanied by the following four supplements: Supplement 1 (ED544556)--This supplement comprises the international version of all TIMSS 2011 background questionnaires. Supplement 2 (ED544557)--This supplement describes any adaptations to the questions in the background questionnaires made by individual TIMSS participants. Supplement 3 (ED544558)--This supplement describes how derived variables were constructed for reporting the TIMSS data. Supplement 4 (ED544559)--This supplement describes the sampling stratification variables for each country. A list of organizations and individuals responsible for TIMSS 2011 is appended. (Individual chapters contain references, exhibits, and footnotes.)