Antitrust law has long condemned tying arrangements when they are imposed by a single dominant firm. However, tying jurisprudence does not recognize that tie-ins can also occur as the result of a conspiracy among competitors. Consequently, antitrust doctrine fails to appreciate the unique anticompetitive dangers of concerted tying arrangements. After providing real-world examples of tying conspiracies, Professor Leslie explains how concerted tying arrangements present a far greater threat to competitive markets than traditional, unilaterally imposed tying arrangements. Because tying jurisprudence evolved without considering the existence or effects of concerted tie-ins, the current test for evaluating the legality of tying arrangements is inappropriately lenient to tying conspiracies. This is completely inconsistent with one fundamental principle of American antitrust law: concerted action should be treated more harshly than unilateral conduct. Finally, the Article advocates per se illegality for tying conspiracies and argues that greater appreciation of concerted tie-ins can inform the ongoing academic debate about tying arrangements more generally.