The What Works Clearinghouse (WWC) seeks to provide educators, policymakers, researchers, and the public with a central and trusted source of scientific evidence for what works in education. The WWC was established in 2002 by the U.S. Department of Education's Institute of Education Sciences (IES). It serves as a decision-making resource by helping the education community locate and recognize credible and reliable evidence. Reviewers working for the WWC assess the quality of studies that evaluate the effectiveness of specific educational products, interventions, practices or approaches. To ensure fairness and consistency in the review of these studies, the WWC uses rigorous and transparent standards for systematically reviewing and synthesizing existing research. From its inception, the WWC reviewed experimental and quasi-experimental group comparison studies. In an effort to expand the pool of rigorous scientific evidence available for review, in 2009, the WWC assembled a panel of national experts in single-case design (SCD) and analysis to develop WWC SCD Standards. This presentation delineates the criteria the WWC uses to identify SCDs and the standards that the WWC uses to evaluate the rigor of SCD studies. The WWC SCD standards are bifurcated into Design and Evidence standards. The Design standards evaluate the internal validity of the design. Reviewers trained in visual analysis then apply the Evidence standards to evaluate the effect of interventions and practices on relevant outcomes. (Contains 1 figure.)