Currently, a de facto global antitrust system, constructed on the basis of emulation of the converging U.S.-E.U. anti-trust/competition law regime is anchoring global laws about unfair business practices as to price fixing and production quotas, inter alia. This de facto system is not yet based de jure in the World Trade Organization or any similar parallel institution. This may be due to the fact that there are several competing theoretical rationales which justify antitrust law. These competing rationales often have conflicting assumptions and the rules which they generate in turn reflect those divergences. Nevertheless, outcomes, rules, and even, finally, the various rationales of the globalizing antitrust law are converging. Competing theories of antitrust, early U.S. populism, Marxism, Corporatism, Ordo-Liberalism, and Neo-Liberalism are exposed here so as to determine where there are any theoretical commonalities. This article makes explicit the competing concerns and assumptions underlying globalizing antitrust law. It argues that the common emerging practical threads of thought are: consumer well being as the standard for determining whether a restriction is reasonable; the recognition that although monopoly may be inevitably more productive, monopoly is not inevitably inefficient or unfair; economic analysis, especially quantitative analysis; and possibly also proportionality analysis to resolve uncertainty. The article explains how the various antitrust rules are consequent to competing concerns and presumptions of the different theories. It concludes that a global antitrust law is possible, and indeed inevitable, due to the globalization of trade. Any eventual "World Competition Law Convention" would best result from a well structured theoretical base. This work provides the needed theoretical overview to help the process of history along, so that global society will emerge out of the conflicts of the past and into prosperty. By exposing the competing ideas and the resulting rules it is hoped that norms generated in the first world center norms will be more rapidly and effectively understood, taken up, and implemented by the global periphery, notably the BRIC countries, and then de jure globally e.g. via an OECD model antitrust convention.