The Sherman Antitrust Act is over a century old, yet debate continues about its original goal. Previous authors, focusing on the substance of the 1890 debate, have reached various conclusions about this goal. Instead of concentrating on the congressional debates, this paper examines the structural context of the Act. The paper argues that the Act is best viewed as a modest statutory extension of the common law. The goals of the common law are then discussed from the viewpoint of the "Law and Economics" school, and the congressional debates on the Sherman Act are also analyzed from this perspective. Using public choice theory, the paper also reviews the political support for the Act and the manner in which Congress chose to have the Act administered. The common law origins of antitrust, the support for, and implementation of the Act all support the conclusion that the Act's goal was economic efficiency.