The What Works Clearinghouse (WWC) examines manuscripts (that is, journal articles, working papers, dissertations, or other publications or pieces of written research presented as complete sets of findings) to determine if they are eligible to be included in a specific review effort. The WWC first determines whether the manuscript contains a single study or multiple studies and whether any other manuscripts discuss the same study or studies. Once this is determined, WWC reviewers screen each study. The WWC is an initiative of the U.S. Department of Education's Institute of Education Sciences. The WWC evaluates research studies that look at the effectiveness of education programs, products, practices, and policies, which the WWC calls "interventions." WWC Process Briefs explain how the WWC does different aspects of its work. This brief discusses: (1) What is a study?; (2) What is the difference between a manuscript and a study?; and (3) When is a study eligible for review by the WWC? [For more information about the review process, see "Standards Handbook. Version 4.0. What Works Clearinghouse™," ED577036 and "Procedures Handbook. Version 4.0. What Works Clearinghouse™," ED577035.]