999 or 112 is used to contact the emergency services upon witnessing or being involved in an emergency. In the United Kingdom, the numbers 999 and 112 both connect to the same service, and there is no priority or charge for either of them.

An emergency can be:

• A person in immediate danger of injury or whose life is at risk
• Suspicion that a crime is in progress
• Structure on fire
• Another serious incident which needs immediate emergency service attendance

On dialling 999 or 112 an operator will answer and ask, "Emergency. Which service?".  Once you answer, the operator will then transfer the call to the appropriate services' own call-taker.

Access to the 999/112 service is provided for the hearing-impaired via Textphone and use of the RNID "Typetalk" relay service. The number is 18000.

999 is also accessible via SMS for pre-registered users.