This article explores the promises and pitfalls of using National Student Clearinghouse (NSC) data to measure a variety of postsecondary outcomes. We first describe the history of the NSC, the basic structure of its data, and recent research interest in using NSC data. Second, using information from the Integrated Postsecondary Education Data System (IPEDS), we calculate enrollment coverage rates for NSC data over time, by state, institution type, and demographic student subgroups. We find that coverage is highest among public institutions and lowest (but growing) among for-profit colleges. Across students, enrollment coverage is lower for minorities but similar for males and females. We also explore two potentially less salient sources of non-coverage: suppressed student records due to privacy laws and matching errors due to typographic inaccuracies in student names. To illustrate how this collection of measurement errors may affect estimates of the levels and gaps in postsecondary attendance and persistence, we perform several case-study analyses using administrative transcript data from Michigan public colleges. We close with a discussion of practical issues for program evaluators using NSC data.