This publication describes the methods and procedures used for the 2017-18 National Postsecondary Student Aid Study, Administrative Collection (NPSAS:18-AC). It also provides information that will be helpful to analysts in accessing and understanding the restricted-use files containing the NPSAS:18-AC data. NPSAS:18-AC includes cross-sectional, nationally representative samples of undergraduate and graduate students enrolled in postsecondary education in the United States. NPSAS:18 AC also includes state-representative samples of undergraduate students in some states, as well as in public 2 year and in public 4 year institution sectors within some states. The study covers topics pertaining to student enrollment with a focus on how individuals and families finance postsecondary education. NPSAS:18-AC is based solely on data collected from administrative data sources and, unlike other NPSAS studies, does not include student survey data.