Transitional Justice is a crucial topic in the study and practice of international relations and international law. Transitional Justice refers to both the process and objectives of societies employing judicial and/or non-judicial mechanisms to address past or even ongoing atrocities and other serious human rights violations. By presenting an overview of Transitional Justice options and the V.S. role in Transitional Justice, and then analyzing four cases studies-the International Military Tribunal, the International Military Tribunal for the Far East, the UN International Criminal Tribunal for the Former Yugoslavia, and the UN International Criminal Tribunal for Rwanda-this thesis seeks to determine why and how the United States has pursued the Transitional Justice option of war crimes tribunals in certain contexts. In so doing, this thesis challenges the dominant approach to explaining U.S. Transitional Justice policy: the "legalist" paradigm developed by Gary Bass. Legalism, a variant of liberalism, postulates that liberal states pursue war crimes tribunals because their decision- makers hold a principled commitment to the rule of law. Bass further argues that illiberal states have never pursued bona fide war crimes tribunals. This thesis develops an alternative theory-"prudentialism"-which contends that any state-liberal or illiberal-may support bona fide war crimes tribunals. A variant of realism, prudential ism postulates that states will pursue tribunals not out of a principled commitment to pursuing justice through the rule of law, but as a result of a case-specific balancing of politics, pragmatics, and normative beliefs. This thesis's analysis of U.S. policy yields several conclusions about these two competing explanations. First, legalism cannot account for the fact that the V.S. has frequently pursued non-legalistic Transitional Justice options instead of or in addition to legalistic Transitional Justice options. Second, legalism fails to explain why, even in instances where the U.S. cooperated in the creation of war crimes trials, those trials did not apply to more suspected atrocity perpetrators from the applicable conflict. Third, legalism fails to explain which of the many types of war crimes trials or tribunals the U .S. has supported in a given context. Finally, legalism does not acknowledge that illiberal states have, in fact, supported bona fide war crimes trials. This thesis demonstrates that U.S. government officials may have held some normative beliefs, but that these individuals did so inconsistently. These beliefs included that at least some suspected atrocity perpetrators should be punished for their offenses. This thesis determines that political and pragmatic factors featured more prominently in the development of U.S. Transitional Justice policy. Political factors driving U.S. Transitional Justice policy included the U.S.'s relationship with its allies and adversaries, particularly at the beginning and end of the Cold War. Pragmatic factors included U.S. officials' desire to obtain access to suspects, witnesses, and evidence; whether the U.S. already had suspects in custody; and path dependency arising from earlier Transitional Justice institutions. I thus determine that, at least in the case of the U.S., prudential ism is a better theory than legalism in explaining its Transitional Justice policy. Future research should examine the Transitional Justice policies of (1) the U.S. in cases beyond the four studied in this thesis, (2) other liberal states, and (3) illiberal states to determine how they have confronted suspected atrocity perpetrators in other instances. If these inquiries revealed that the U.S. and other liberal states have often supported non-legalistic options and that illiberal states have occasionally supported legalistic Transitional Justice options, then those findings would further call legalism into question.