It is perhaps more important today than ever for stakeholders to understand the key approaches and methods for measuring the accuracy of the U.S. decennial census. The 2020 Census faces extraordinary challenges that will impact its fairness and accuracy. Flawed census numbers may skew political representation and the allocation of federal funds for the next decade and affect an array of other crucial uses of census data. To help stakeholders better engage in public discussions of census accuracy and related actions, this report introduces measures and methods for evaluating census accuracy, assesses their relative strengths and weaknesses, and provides key historical context needed for interpreting the results of the census.