Education decisionmakers need access to the best evidence about the effectiveness of education interventions, including practices, products, programs, and policies. It can be difficult, time consuming, and costly to access and draw conclusions from relevant studies about the effectiveness of interventions. The What Works Clearinghouse (WWC) addresses the need for credible, succinct information by identifying existing research in education, assessing the quality of this research, and summarizing and disseminating the evidence from studies that meet WWC standards. This "WWC Procedures and Standards Handbook, Version 5.0," provides a detailed description of how the WWC reviews studies that meet eligibility requirements for a WWC review. Version 5.0 of the "Handbook" replaces the two documents used since October 2020, the "What Works Clearinghouse Procedures Handbook, Version 4.1" (ED602035) and the "What Works Clearinghouse Standards Handbook, Version 4.1" (ED602036). "WWC Procedures and Standards Handbook, Version 5.0" is organized such that most frequently used information appears in earlier chapters. The need for technical knowledge of research design increases in subsequent chapters. Chapter I provides a general overview of WWC procedures and standards. The overview is intended for readers who need a working knowledge of how the WWC reviews studies but who will not conduct study reviews or design studies intended to meet WWC standards. Chapter II describes procedures for screening studies for eligibility. Chapter III describes procedures and standards for reviewing findings from randomized controlled trials and quasi-experimental designs. Chapter IV describes procedures and standards for reviewing findings from studies that use a regression discontinuity design. Chapter V focuses on reviewing findings from group design studies that use advanced methodological procedures, such as randomized controlled trials that estimate complier average causal effects, and analyses that impute missing data. Chapter VI describes procedures and standards for reviewing findings from single-case design studies. Finally, Chapter VII describes procedures for synthesizing and characterizing findings from reviews of individual studies and in intervention reports and practice guides. The "Handbook" concludes with technical appendices. These appendices provide details on the procedures underlying the review process; for example, the calculation and estimation of effect sizes and other computations used in WWC reviews. In addition, the technical appendices include information on procedures underlying the development of WWC products, such as how the WWC identifies studies to include in intervention reports and practice guides.