The Trends in International Mathematics and Science Study (TIMSS) is an international comparative study designed to measure trends in mathematics and science achievement at the fourth and eighth grades, as well as to collect information about educational contexts (such as students' schools, teachers, and homes) that may be related to student achievement. TIMSS has been administered every 4 years since 1995, with the sixth and most recent administration, in 2015, providing a 20-year trend line. The United States has participated in every administration of TIMSS, which includes 1995, 1999, 2003, 2007, 2011, and 2015 for the eighth grade and all but 1999 for the fourth grade (when it was not administered internationally). TIMSS is designed to align broadly with mathematics and science curricula in the participating education systems and, therefore, to reflect students' school-based learning. Because it is an international study, TIMSS provides valuable benchmarking information on how U.S. students compare to students around the world. The U.S. TIMSS and TIMSS Advanced 1995 & 2015 Technical Report and User's Guide provides an overview of the design and implementation of the Trends in International Mathematics and Science Study (TIMSS) 2015 and TIMSS Advanced 2015 in the United States and one participating benchmarking state: Florida. Part 1 of the report contains the full report; Appendix A: TIMSS 2015 and TIMSS Advanced 2015 Reruitment Materials; Appendix B: Informational Materials; and Appendix C: Field Staff Training Materials. Appendix D: TIMSS 2015 and TIMSS Advanced 2015 Questionnaires begins in Part 2, continues in Part 3, and ends in Part 4. Part 4 also contains Appendix E: TIMSS 2015 and TIMSS Advanced 2015 Questionnaire Adaptations; Appendix F: TIMSS 2015 Nonresponse Bias Analysis: Grades 4 and 8; and Appendix G: TIMSS 2015 Nonresponse Bias Analysis: Advanced. ["Trends in International Mathematics and Science Study (TIMSS). U.S. TIMSS 2015 and TIMSS Advanced 1995 & 2015 Technical Report and User's Guide. Part 2. NCES 2018-020," see ED589558; "Trends in International Mathematics and Science Study (TIMSS). U.S. TIMSS 2015 and TIMSS Advanced 1995 & 2015 Technical Report and User's Guide. Part 3. NCES 2018-020," see ED589559; and "Trends in International Mathematics and Science Study (TIMSS). U.S. TIMSS 2015 and TIMSS Advanced 1995 & 2015 Technical Report and User's Guide. Part 4. NCES 2018-020," see ED589560.]