This essay analyzes and compares different approaches to the problem of legal precedent. If judges reasoned flawlessly, the ideal approach to precedent would give prior judicial opinions only the weight they naturally carry in moral reasoning. Given that judges are not perfect reasoners, the best approach to precedent is one that treats rules established in prior decisions as authoritative for later judges. In comparison to the natural model of precedent, a rule-based model minimizes error. A rule-based model is also superior to several popular attempts at compromise, which call on judges to reason from the results of prior cases or from principles immanent in the body of precedent. The principal drawback of a rule-based model of precedent is its seeming resistance to change. After defending the rule model against its competitors, we discuss a variety of refinements that clarify the model and make it more amenable to legal reform. Topics covered include identification of precedent rules, preconditions for authority, decision-making in the absence of a precedent rule, and overruling.