The chapters in this online volume comprise the TIMSS & PIRLS International Study Center's technical report of the methods and procedures used to develop, implement, and report the results of TIMSS 2019. There were various technical challenges because TIMSS 2019 was the initial phase of the transition to eTIMSS, with approximately half the countries administering the assessment via computer and the remaining countries still using the paper-and-pencil format. Thus, the TIMSS 2019 assessments and questionnaires were developed and administered in both "e" and paper formats. Then, a multi-faceted approach to the achievement scaling enabled reporting comparable trends for both sets of countries on the TIMSS scales. The success of TIMSS 2019 is a tribute to all those involved, including the TIMSS & PIRLS International Study Center, IEA Amsterdam, IEA Hamburg, Statistics Canada, and the National Research Coordinators and their teams in the participating countries.