A full-scale public health response to disasters must attend to both the physical and mental health needs of affected communities. Public health preparedness efforts can be greatly expanded to address the latter set of needs, particularly in light of the high ratio of psychological to physical casualties that often rapidly overwhelms existing mental health response resources in a large-scale emergency. Psychological first aid--the provision of basic psychological care in the short term aftermath of a traumatic event--is a mental health response skill set that public health personnel can readily acquire with proper training. The application of psychological first aid by public health workers can significantly augment front-line community-based mental health responses during the crisis phase of an event. To help achieve this augmented response, we have developed a set of psychological first aid intervention competencies for public health personnel. These competencies, empirically grounded and based on best practice models and consensus statements from leading mental health organizations, represent a necessary step for developing a public health workforce that can better respond to the psychological needs of impacted populations in disasters.