The clinical provision of medical care by emergency medical services (EMS) providers in the out-of-hospital environment and the operation of EMS systems to provide that care are unique in the medical arena. There is a substantive difference in the experience of individuals who provide medical care in the out-of-hospital setting and the experience of those who provide similar care in the hospital or other clinical settings. Furthermore, physicians who provide medical direction for EMS personnel have a clinical and oversight relationship with EMS personnel. This relationship uniquely qualifies EMS medical directors to provide expert opinions related to care provided by nonphysician EMS personnel. Physicians without specific EMS oversight experience are not uniformly qualified to provide expert opinion regarding the provision of EMS. This resource document reviews the current issues in expert witness testimony in cases involving EMS as these issues relate to the unique qualifications of the expert witness, the standard of care, and the ethical expectations.