Why are some judicial opinions widely cited while others languish in disuse? We theorize that both efficiency and persuasiveness structure the effect an opinion has on legal development. Precedents that are both unanimous and well-grounded in the law have greater persuasive value while citation to precedents that are easier to read allows a judge to craft an opinion more efficiently. We estimate the effect of an opinion's readability, the number of footnotes it contains, its use of precedent, and whether it contains a dissenting opinion on the number of times each year the opinion is cited and its vitality in the United States Supreme Court, the precedent's own court, the precedent's sister courts, the precedent's directly subordinate courts, and all remaining state and federal courts. We thus track vertical influence both up and down the judicial hierarchy and evaluate horizontal influence both within the precedent's jurisdiction and across jurisdictional lines.