Syllabus
2. Under the Federal Arbitration Act, an ambiguous agreement cannot provide the necessary contractual basis for concluding that the parties agreed to submit to class arbitration. Pp. 5–12.
(a) “Arbitration is strictly a matter of consent,” Granite Rock Co. v. Teamsters, 561 U. S. 287, 299 (internal quotation marks omitted), and the task for courts and arbitrators is “to give effect to the intent of the parties,” Stolt-Nielsen, 559 U. S., 684. In carrying out that responsibility, it is important to recognize the “fundamental” difference between class arbitration and the individualized form of arbitration envisioned by the FAA. Class arbitration “sacrifices the principal advantage of arbitration—its informality—and makes the process slower, more costly, and more likely to generate procedural morass than final judgment.” Concepcion, 563 U. S., at 348. Because of such “crucial differences,” Stolt-Nielsen, 559 U. S., at 687, this Court has held that courts may not infer consent to participate in class arbitration absent an affirmative “contractual basis for concluding that the party agreed to do so,” id., at 684. Silence is not enough. Id., at 687. That reasoning controls here. Like silence, ambiguity does not provide a sufficient basis to conclude that parties to an arbitration agreement agreed to “sacrifice[] the principal advantage of arbitration.” Concepcion, 563 U. S., at 348. This conclusion aligns with the Court’s refusal to infer consent when it comes to other fundamental arbitration questions. See, e. g., First Options of Chicago, Inc. v. Kaplan, 514 U. S. 938, 945. Pp. 6–9.