In the landmark case Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), the Supreme Court of the United States articulated the admissibility standard for expert evidence. In jurisdictions that have adopted the Daubert standard, trial court judges must make difficult decisions regarding the admissibility of proffered expert evidence. Although all federal courts and nearly all state courts use the Daubert standard, we know little about how judges fulfill their gatekeeping role when making admissibility decisions. This chapter reviews the empirical and theoretical considerations regarding how judges in Daubert jurisdictions determine which proffered expert evidence should be admitted. After reviewing the standards governing the admissibility of expert testimony, which includes a discussion of the Federal Rules of Evidence, Daubert, and related cases, the chapter provides a discussion of each Daubert criterion, including the available evidence relating to judges’ understanding of those criteria. It then discusses the heuristics and biases that affect judicial decision-making. The chapter concludes with a discussion of implications for practice and research.