While there has been significant political discussion as to the utility and/or risks associated with the doctrine of preemption, the legal debate has to date been fairly limited. Few if any have sought to define the legal parameters of the doctrine. The purpose of this article is to help define the appropriate legal parameters for use of the doctrine. This article will first review the strategic rationale for preemption, and a detailed definition of the modern doctrine. This will be followed by a review of the United States’ government’s legal rationale and a review of the emerging legal debate before discussing the applicable parameters. The article will conclude with the argument that in order to guard against the unwarranted application of the doctrine a specific set of clearly defined criteria must be developed for its use.