This supplement describes national adaptations made to the international version of the PIRLS/prePIRLS 2011 background questionnaires. This information provides users with a guide to evaluate the availability of internationally comparable data for use in secondary analyses involving the PIRLS/prePIRLS 2011 background variables. Background questionnaire adaptations include questions that countries were required to adapt, questions that were not administered, and questions that countries modified to suit their national context. National adaptations are presented in four sections--one for each of the PIRLS/prePIRLS 2011 background questionnaires: (1) Student Questionnaire; (2) Home Questionnaire (Learning to Read Survey); (3) Teacher Questionnaire; and (4) School Questionnaire. Within each section, PIRLS national adaptations are listed first, followed by prePIRLS. For each background question that was adapted, a national entry is included if the version of the question administered in a country was different from the international version. For each question, the following information is provided: (1) Question number; (2) Question stem and response options; (3) Variable name(s); and (4) National adaptation, listed by country. [For the "PIRLS 2011 User Guide for the International Database," see ED544357. For Supplement 1, see ED544359. For Supplement 3, see ED544361. For Supplement 4, see ED544358.]