Vol. 123 No. 2 Chicago School theorists have argued that tying cannot create anticompetitive effects because there is only a single monopoly profit. Some Harvard School theorists have argued that tying doctrine’s quasi—per se rule is misguided because tying cannot create anticompetitive effects without foreclosing a substantial share of the tied market. This Article shows that both positions are mistaken. Even without a substantial foreclosure share, tying by a firm with market power generally increases monopoly profits and harms consumer and total welfare, absent offsetting efficiencies. The quasi—per se rule is thus correct to require tying market power and a lack of offsetting efficiencies, but not a substantial tied foreclosure share. However, the quasi—per se rule should have an exception for products with a fixed ratio that lack separate utility, because those conditions generally negate anticompetitive effects absent a substantial foreclosure share. Cases meeting this exception should instead be governed by a traditional rule of reason that requires a substantial foreclosure share or effect.