Introduction in the United States
In January of 1968, the American Telephone and Telegraph Company announced that within its serving areas the digits 9-1-1 were available for installation on a national scale as the single emergency telephone number. Although numerous public safety officials and individuals at various government organizational levels had long expressed keen interest in the establishment of such a number, the AT&T announcement was primarily prompted by the 1967 recommendation of The President's Commission on Law Enforcement and Administration of Justice that "wherever practical a single (police emergency) number should be established within a metropolitan area and preferably over the entire United States". Further stimulus toward the creation of a nationwide number was provided by the Commission on Civil Disorders and Federal Communications Commission which urged the telephone industry to provide a three-digit emergency telephone number. These various recommendations had in turn received impetus from growing public concern over the increase in crime, accidents, and medical emergencies and from Federal Government awareness that current emergency reporting methods were inadequate and that in a population as large and as mobile as ours, a common emergency number made sense.
In response to these concerns, the Federal Government in March of 1973, through the Office of Telecommunications Policy, Executive Office of the President, issued National Policy Bulletin Number 73-1 endorsing the concept of 9-1-1 and urging it's nationwide implementation.
The choice of the specific number, 9-1-1, was based primarily on cost factors, the comparative ease with which the telephone company equipment could be modified to accept the number and on other considerations which indicated that the combination of the digits 9-1-1 would be easily remembered and dialed by most persons.

How did the idea develop?

Great Britain was the first country to establish a universal emergency telephone number. Since 1937 any individual in the United Kingdom has been able to dial 999, receive a prompt response, and have his or her request for assistance (police, fire, ambulance) quickly and efficiently directed to the proper agency. In developing similar systems, Belgium has adopted 900 as its uniform emergency number. Denmark has provided 000, and in Sweden the caller dials 80 000. Several of these systems are directed primarily toward the provision of emergency medical services. Other countries which have provided three or two-digit emergency number, either universally or for large population segments, include West Germany; Caracas, Venezuela, which developed its system in 1963 with the help of the United States; and Winnipeg, Canada, where the system has been in service since 1959. Canada is currently developing a national system utilizing 91-1 and Japan has implemented 1-1-9 throughout their country.