Managed by the Agency for Healthcare Research and Quality, the Healthcare Cost and Utilization Project (HCUP, pronounced H-Cup) is a collection of data sets that represent the largest collection of administrative, longitudinal health care data in the United States. The data represent all-payer encounter-level information beginning in 1988 and is a collaborative effort between state data organizations, hospital associations, private data organizations, and the federal government. The stated objective of the project is to 鈥渃onduct and translate research to inform decision making and improve health care delivery.鈥� Because an extensive description of all HCUP data sets is beyond the scope of this review, we will focus on the National Inpatient Sample (NIS, formerly Nationwide Inpatient Sample) as it relates to surgical research. This guide is an introduction; interested readers can explore the resources available on the HCUP website (/). Many of the ideas we discuss will be applicable to the entire HCUP suite (Table).