This paper reviews the antitrust treatment of patent-pooling and cross-licensing arrangements from E. Bement & Sons v. National Harrow Co., decided in 1902, to the recent Department of Justice business review letters on the MPEG and DVD patent pools. I examine the factors that the courts identified as pertinent to the antitrust outcome and compare them to the competitive factors identified in the DOJ/FTC Antitrust Guidelines for the Licensing of Intellectual Property. Until recently, the competitive relationship of the patents was not a major determinant of the antitrust outcome in most cases. Instead, the courts have focused on restrictive licensing terms that affect downstream prices. I consider the logic of this approach to evaluating antitrust liability. I also propose an approach to evaluating the antitrust risks of arrangements that combine potentially blocking patents.