This article examines contestations over psychiatric knowledge during the legal proceedings of Guantanamo detainees. First, the US government's use of mental health professionals to introduce reconfigured definitions of torture is probed. Next, the government's concerns around ascertaining competency to stand trial is reviewed. The article then examines debates over the appropriateness of the death penalty in the cases of five Guantanamo detainees, all suspected of masterminding the 9/11 attacks. The article concludes by exploring how critical anthropology can help elucidate the state's exercise of power over people and their bodies (“biopower”) – an exercise governed in part by legal institutions. Throughout the article, psychiatry is viewed as a discourse that bridges US medical and legal understandings of the body while recognizing that conceptions of the body, life, and death that vary across cultures.