Resale price maintenance (RPM) is a practice whereby the manufacturer of the wholesaler restricts the selling price by the retailer. Vertical RPM agreements are per se illegal under the Sherman Antitrust Act. The trend, in court decisions, however, has been to weigh the pro-competitive effects against the anti-competitive effects, the rule of reason, rather than to consider such agreements illegal per se. This paper discusses that rule of reason should always be applied to vertical RPM agreements.