An area code is usually a three-digit number that identifies which part of the country a phone number comes from. When you dial a phone number in the United States or Canada, the area code comes first: for example, in the number (415) 555-1234, the 415 is the area code for San Francisco.

Area codes were introduced in 1947 to make long-distance calling easier as more Americans got telephones. Before area codes, operators had to manually connect calls between cities, which was slow and complicated. With area codes, the telephone system could automatically route calls to the right region.

Originally, each area code covered a large geographic area. New York City got 212, Los Angeles got 213, and Chicago got 312. The middle digit was always 0 or 1, which helped old mechanical telephone switches recognize them. As the population grew and more people needed phone numbers, cities ran out of available numbers and had to add new area codes. Today, Manhattan alone has several different area codes.

Even though cell phones have made area codes less meaningful (you can keep your number when you move), they still tell you something about where a number originated. Some people feel attached to their area code as a badge of where they're from, the way someone might proudly say “I'm a 617” to show they're from the Boston area.