Trauma has wide-reaching implications for survivors and for those who come to their aid. First respond-ers may experience trauma as a direct survivor (of threats to the worker's own life or psychological or physical integrity) or as a result of coming to the aid of those in desperate need (e.g., post–natural disaster or serious accident). Regardless of the cause of an individual's traumatization, there is clear evidence for the potential for both positive and negative posttrauma consequences and first responders are no exception. In this entry, the term first responder is defined, followed by a discussion of salient variables that affect the mental health of those people who come to the aid of others at their critical hour of need.