This article is about non-signatories to arbitration agreements. The issue I address concerns a difference in the approach taken by U.S. courts when a non-signatory seeks to rely on an arbitration clause against a signatory versus when a signatory seeks to rely on an arbitration clause against a non-signatory. When it comes to one particular non-signatory theory—the "intertwined claims" estoppel theory (about which more below)—U.S. courts hold that a non-signatory may rely upon an arbitration clause against a signatory, but not the other way around.