An emergency is an urgent, unexpected, and usually dangerous situation that poses an immediate risk to health, life, property, or environment and requires immediate action. Emergencies can be self-evident, such as a natural disaster that threatens many lives, or smaller incidents that require an observer or affected party to decide whether it qualifies as an emergency. The precise definition of an emergency, the agencies involved, and the procedures used vary by jurisdiction, and this is usually set by the government, whose agencies (emergency services) are responsible for emergency planning and management.

The dictionary definition of an emergency is "a serious, unexpected, and often dangerous situation requiring immediate action". Emergencies can include natural disasters, accidents, and crises. An incident, to be an emergency, conforms to one or more of the following: it poses an immediate threat to life, health, property, or environment; it has already caused loss of life, health detriments, property damage, or environmental damage; or it has a high probability of escalating to cause immediate danger to life, health, property, or environment.

Emergency Medical Services (EMS) is a system that responds to emergencies in need of highly skilled pre-hospital clinicians. EMS clinicians respond to all kinds of emergencies, hazards, and natural and man-made disasters, and they often work side-by-side with public safety colleagues in law enforcement and the fire service, with the primary mission of providing emergency medical care. EMS clinicians also play an important role in mental health and behavioral health crisis services.