Since the issue first arose in earnest in the 1970s, courts have struggled to create rules for causation in toxic tort cases that are both consistent with longstanding tort principles and fair to all parties. Faced with conflicting and often novel expert testimony, scientific uncertainty, the gap between legal and scientific culture, and unprecedented claims for massive damages, common-law courts needed time to adjust and accommodate themselves to the brave new world of toxic tort litigation. Eventually, however, courts around the country reached a broad consensus on what is required for a toxic tort plaintiff to meet his or her burden of proof. While there is a voluminous scholarly literature on various aspects of toxic tort litigation, this Article's unique contribution is to articulate the new consensus on causation standards, document and criticize the various ways plaintiffs attempt to evade these standards, and defend the courts' adherence to traditional notions of causation against their critics. Part I of this Article explains that to prove causation in a toxic tort case, a plaintiff must show that the substance in question is capable, in general, of causing the injury alleged, and also that exposure to the substance more likely than not caused his injury. When a plaintiff was exposed to a single toxin from multiple sources, to prove causation by a specific defendant the plaintiff must show that the actions of that defendant were a “substantial factor” in causing the alleged harm. Part II discusses plaintiffs' attempts to evade these standards by hiring experts to present various types of unreliable causation evidence. Examples of such evidence include testimony based on high-dose animal studies, anecdotal case reports, analogizing from the known effects of “similar” chemicals, preliminary epidemiological studies that have not been peer-reviewed, and differential etiologies used to “rule in” an otherwise unknown causal relationship. Additionally, when multiple defendants have contributed to the plaintiffs' exposure to a potentially toxic substance, plaintiffs often present experts who claim, with no reliable scientific grounding, that the level of exposure (“dose”) is irrelevant to causation. Part III of this Article argues that courts should be steadfast in requiring toxic tort plaintiffs to meet their burden of proof. Traditional tort principles require that plaintiffs bear the burden of proving actual causation by a preponderance of the evidence, not merely that they were exposed to a risk. To hold otherwise and essentially shift the burden to defendants to disprove causation would open the floodgates to all manner of speculative claims, with potentially devastating consequences for Americans' well-being. Similarly, with regard to cases in which a plaintiff alleges injury after exposure to a toxin from multiple sources, a given defendant may only be held liable if the plaintiff proves by a preponderance of the evidence that exposure to that defendant's products was a “substantial factor” in causing that injury. To hold otherwise would amount to an implicit adoption of a system of broad, collective liability that courts have rejected when the issue has been raised explicitly. This section concludes by discussing the negative consequences that arise from speculative toxic tort litigation unsupported by reliable scientific evidence.