Mental health and psychosocial support (MHPSS) has become an increasingly common form of humanitarian aid in disasters and emergencies, particularly since the publication of the influential IASC Guidelines in 2007. Despite increased acceptance of and attention to MHPSS within the humanitarian field, fundamental questions about the logic and practice of MHPSS remain unresolved. Drawing from and contributing to scholarly literature in feminist political geography and science and technology studies, this dissertation investigates the policies, politics, and practice of MHPSS in emergencies through qualitative interviewing, archival research, and content and discourse analysis of standards and guidelines for this form of humanitarian aid. Previous scholarship critiquing the inclusion of mental health and psychosocial interventions within emergency humanitarian response does not adequately account for the central divisions and debates that have characterized the MHPSS field for decades—or for the ontological and epistemological multiplicity underlying these debates. In contrast with framings of MHPSS as a field that is characterized by professional consensus, I argue that key questions about MHPSS as a domain of expert knowledge and practice remain unresolved. This lack of consensus stems, in part, from a tension between conceptualizations of MHPSS as a standardized, technical practice, and as an intimate and humane form of care. This research adds depth and nuance to critical scholarship on MHPSS in humanitarian emergencies by analyzing three interrelated areas of dissensus within the humanitarian field: trauma and PTSD as objects of expert intervention in disasters and emergencies; the role of medicalized mental health care in humanitarian emergency response; and systems of classification that are foundational to the practice of MHPSS in emergencies.