From e-commerce to electronic tax filing to securing office building entry, the need to verify identity and authorize physical access has driven the development of increasingly advanced authentication systems. Almost all these systems use personal information (in many cases, personally identifiable information), which raises numerous privacy concerns. In early 2003, the National Academy of Sciences' Committee on Authentication Technologies and Their Privacy Implications issued a report addressing this broad set of issues. This article summarizes some of the key insights from that report.