Health services research (HSR) in emergency medicine assesses whether effective care reaches the right patients, in time, across prehospital, emergency department, and regional referral pathways. This chapter outlines a practical HSR agenda for emergency care focused on application and measurement. The needs–demand–supply triad explains mismatches during surges, disasters, and prolonged constraints and highlights levers—triage, regionalization, and alternative pathways (e.g., general practitioner cooperatives, hospital-attached primary care, and after-hours or home-based services). Two recurring problems—rising low-acuity ambulance use among older adults and delays in time-sensitive care—illustrate how organization and access shape outcomes. Key indicators for cross-hospital and cross-regional comparison include access and transport times, handoff intervals, treatment timeliness, clinical outcomes, functional status, and patient satisfaction. These approaches enable rigorous evaluation and targeted redesign of emergency care systems.