Progress in International Reading Literacy Study (PIRLS) provides international comparative data about students' reading achievement after four years of primary schooling, while also measuring trends over time, monitoring curricular implementation, and identifying promising instructional practices. Conducted on a regular 5-year cycle, PIRLS has assessed reading achievement in 2001, 2006, and 2011. PIRLS, along with its sister study prePIRLS introduced in 2011, collects a rich array of background information to provide comparative perspectives on trends in reading achievement in the context of different educational systems, school organizational approaches, and instructional practices. As a new initiative in 2011, IEA has developed the prePIRLS assessment in response to the needs of the growing population of countries requiring the kind of information provided by PIRLS, but whose students are earlier in the process of learning to read than is expected by the PIRLS assessment. The prePIRLS assessment has shorter and easier reading texts than PIRLS, and places less emphasis on higher-order reading skills. Three countries participated in the 2011 launch of prePIRLS. To support and promote secondary analyses aimed at improving reading education in the primary grades, the PIRLS 2011 International Database makes available to researchers, analysts, and other users the data collected and processed by the PIRLS project, as well as the data from the prePIRLS assessment. In order to work effectively with the PIRLS and prePIRLS 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 PIRLS 2011 International Database. In addition to this introduction, the User Guide includes the following three chapters: Chapter 2--This chapter introduces the International Association for the Evaluation of Educational Achievement (IEA) International Database (IDB) Analyzer software (IEA, 2012) and presents examples of analyses with the PIRLS 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 (SAS Institute, 2011) statistical software system 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 (ED544359)--This supplement comprises the international version of all PIRLS 2011 background questionnaires. Supplement 2 (ED544360)--This supplement describes any adaptations to the questions in the background questionnaires made by individual PIRLS and prePIRLS participants. Supplement 3 (ED544361)--This supplement describes how derived variables were constructed for reporting the PIRLS data. Supplement 4 (ED544358)--This supplement describes the sampling stratification variables for each country. A list of organizations and individuals responsible for PIRLS 2011 is appended. (Individual chapters contain footnotes and exhibits.)