This Article examines the role of expertise in judicial opinion assignment and offers four contributions: First, this Article develops a general theory of opinion assignment on multimember courts. Second, this Article uses that theory to predict how expertise might influence opinion assignment. Third, because the theory advanced in this Article suggests that the courts of appeals are far more likely to witness experience-based opinion assignment than is the Supreme Court, this Article contributes to an understanding of opinion assignment practices in this understudied area. Fourth, this Article identifies two settings in which the theory this Article advances should have observable implications, and this Article proceeds to test those implications empirically. It finds that, in the years following the initial adoption of the Sentencing Guidelines, circuit judges who were Sentencing Commissioners were more likely to have assigned to them opinions raising sentencing issues. It also finds that circuit judges who previously served as bankruptcy judges were more likely to have bankruptcy cases assigned to them. The Guidelines setting, moreover, allows for a natural experiment, in that we can test whether judges who served as Commissioners saw disproportionate levels of opinion assignment in criminal cases before the Guidelines took effect; it turns out, consistent with the theory, that they did not.