The Bail Reform Act of 1984 changed the law dictating release and detention decisions in Federal court. Since its passage, few studies have examined judicial decisionmaking in this context. Legal research enables one to account for the structure and interpretation of Federal detention laws and to analyze previously neglected measures of legal factors in the author's analyses. The authors used U.S. Sentencing Commission data on a sample of defendants who were sentenced in 2007 (N=31,043). The authors found that legal factorsparticularly length of criminal history, having committed a violent or otherwise serious offense, and having committed the offense while under supervision of the criminal justice systemhave the strongest relationships with the presentence detention outcome. A defendant's age, race, and ethnicity have weaker relationships with detention. When the authors compared defendants who were similarly situated with respect to legal factors, the probability of detention was similar regardless of age, race, and ethnicity. Abstract published by arrangement with Taylor and Francis.