Legal clarity is important to understand and measure because of its connection to the rule of law. We provide the first systematic examination of the clarity of Supreme Court opinions and discover five important results. First, certain justices systematically craft clearer opinions than others. Justices Scalia and Breyer write the clearest opinions, while Justice Ginsburg consistently writes the most complex opinions. Second, ideology does not predict clarity in majority or concurring opinions. Third, all justices write clearer dissents than majority opinions, while minimum winning coalitions produce the clearest majority opinions. Fourth, justices across the board write clearer opinions in criminal procedure cases than in any other issue area. Finally, opinions that formally alter Court precedent render less clear law, potentially leading to a cycle of legal ambiguity.