Antitrust law is moving away from rules (ex ante, limited factor liability determinants) and toward standards (ex post, multi-factor liability determinants). This movement has important consequencesfor the structure of antitrust adjudication, including shifting ultimate decision-making down the legal hierarchy (in the direction ofjuries, trial courts sitting as factfinders, and administrative agencies) and increasing the importance of economic experts. The efficiency consequences of this trend are often negative. Specifying liability determinants as open-ended, unpredictable standards increases litigation costs, chills socially beneficial industrial practices, allocates decisionmaking on microeconomic policy to unqualified juries, andfacilitates strategic misuse of antitrust litigation by rent-seeking competitors. Instead offollowing a generalized preference for standards, courts should consider five factors in choosing the ex ante precision of liability determinants: (1) whether the lawsuit was brought by the government or a private party; (2) whether the legal determinant would create liability or immunize against it; (3) whether the remedy sought is prospective (i.e., injunctive) or retrospective (i.e., damages); (4) whether the conduct is idiosyncratic or paradigmatic; and (5) whether the misconduct alleged is collusion or exclusion.