Emergency medicine is the medical speciality concerned with the care of illnesses or injuries requiring immediate medical attention. Emergency physicians (often called “ER doctors” in the United States) continuously learn to care for unscheduled and undifferentiated patients of all ages. As first-line providers, in coordination with Emergency Medical Services, they are primarily responsible for initiating resuscitation and stabilization and performing the initial investigations and interventions necessary to diagnose and treat illnesses or injuries in the acute phase. Emergency physicians generally practise in hospital emergency departments, pre-hospital settings via emergency medical services, and intensive care units. Still, they may also work in primary care settings such as urgent care clinics.

Emergency medical services (EMS), also known as ambulance services or paramedic services, are emergency services that provide urgent pre-hospital treatment and stabilisation for serious illness and injuries and transport to definitive care. They may also be known as a first aid squad, FAST squad, emergency squad, ambulance squad, ambulance corps, life squad or by other initialisms such as EMAS or EMARS.

In most places, the EMS can be summoned by members of the public (as well as medical facilities, other emergency services, businesses and authorities) via an emergency telephone number which puts them in contact with a control facility, which will then dispatch a suitable resource for the situation. Ambulances are the primary vehicles for delivering EMS, though some also use cars, motorcycles, aircraft, or boats. EMS agencies may also operate a non-emergency patient transport service, and some have rescue squads to provide technical rescue services.

An emergency department (ED), also known as an accident & emergency department (A&E), emergency room (ER), emergency ward (EW) or casualty department, is a medical treatment facility specializing in emergency medicine, the acute care of patients who present without prior appointment; either by their own means or by that of an ambulance. The emergency department is usually found in a hospital or other primary care centre.

Due to the unplanned nature of patient attendance, the department must provide initial treatment for a broad spectrum of illnesses and injuries, some of which may be life-threatening and require immediate attention. In some countries, emergency departments have become important entry points for those without other means of access to medical care.

Primary care is the day-to-day healthcare given by a health care provider. Typically this provider acts as the first contact and principal point of continuing care for patients within a healthcare system, and coordinates other specialist care that the patient may need. Patients commonly receive primary care from professionals such as a primary care physician (general practitioner or family physician), a physician assistant, or a nurse practitioner. In some localities, such a professional may be a registered nurse, a pharmacist, a clinical officer, or an Ayurvedic or other traditional medicine professional (as in parts of Asia). Depending on the nature of the health condition, patients may then be referred for secondary or tertiary care.