In an effort to expand the pool of scientific evidence available for review, the What Works Clearinghouse (WWC) assembled a panel of national experts in single-case design (SCD) and analysis to draft SCD Standards. SCDs are adaptations of interrupted time-series designs and can provide a rigorous experimental evaluation of intervention effects. SCDs can provide a strong basis for establishing causal inference, and these designs are widely used in applied and clinical disciplines in psychology and education, such as school psychology and the field of special education. In this paper, the panel provides an overview of SCDs, specifies the types of questions that SCDs are designed to answer, and discusses the internal validity of SCDs. The panel then proposes SCD Standards to be implemented by the WWC. The Standards are bifurcated into Design and Evidence Standards. The Design Standards evaluate the internal validity of the design. Reviewers assign the categories of "Meets Standards," "Meets Standards with Reservations," and "Does not Meet Standards" to each study based on the Design Standards. Reviewers trained in visual analysis will then apply the Evidence Standards to studies that meet standards with or without reservations, resulting in the categorization of each outcome variable as demonstrating "Strong Evidence," "Moderate Evidence," or "No Evidence." Appended are: (1) Attrition Diagram; and (2) Visual Analysis. (Contains 1 table, 11 figures and 16 footnotes.)