The Eastern Time Zone (ET) is a time zone encompassing part or all of 22 states in the eastern part of the contiguous United States, parts of eastern Canada, the state of Quintana Roo in Mexico, Panama in Central America, and certain Caribbean and Atlantic islands, along with certain countries and parts of countries in South America. Places that use Eastern Standard Time (EST) when observing standard time (autumn/winter) are five hours behind Coordinated Universal Time (UTC−05:00).

Eastern Daylight Time (EDT), when observing daylight saving time (spring/summer), is four hours behind Coordinated Universal Time (UTC−04:00).

In the northern parts of the time zone, on the second Sunday in March, at 2:00 a.m. EST, clocks are advanced to 3:00 a.m. EDT leaving a one-hour "gap". On the first Sunday in November, at 2:00 a.m. EDT, clocks are moved back to 1:00 a.m. EST, thus "duplicating" one hour. Southern parts of the zone (Panama and the Caribbean) do not observe daylight saving time.

The largest city in the Eastern Time Zone is New York; the New York metropolitan area is the largest metropolitan area in the zone.

The boundaries of the Eastern Time Zone have moved westward since the Interstate Commerce Commission (ICC) took over time-zone management from railroads in 1938. For example, the easternmost and northernmost counties in Kentucky were added to the zone in the 1940s, and in 1961 most of the state went Eastern. In 2000, Wayne County, on the Tennessee border, switched from Central to Eastern.^[1] In March 2018, the Florida Legislature passed a bill requesting authorization from Congress for year-round daylight saving time, which would effectively put Florida on Atlantic Standard Time year-round (except for west of the Apalachicola River, which would be on Eastern Standard Time year-round).^[2]

The Uniform Time Act of 1966, ruled that daylight saving time would run from the last Sunday of April until the last Sunday in October in the United States.^[3] The act was amended to make the first Sunday in April the beginning of daylight saving time as of 1987.^[3] The Energy Policy Act of 2005 extended daylight saving time in the United States beginning in 2007. So local times change at 2:00 a.m. EST to 3:00 a.m. EDT on the second Sunday in March and return at 2:00 a.m. EDT to 1:00 a.m. EST on the first Sunday in November.^[3] In Canada, the time changes as it does in the United States.^[4][5]

In Canada, the following provinces and territories are part of the Eastern Time Zone:

All observe daylight saving time in sync with the United States, with very localized exceptions.

The boundary between time zones is set forth in the Code of Federal Regulations, with the boundary between the Eastern and Central Time Zones being specifically detailed at 49 CFR 71.^[6]

Seventeen states and Washington, D.C. are located entirely within the Eastern Time Zone. They are:

Five states are partly in the Eastern Time Zone, with the remaining portions in the Central Time Zone. They are:

Eastern Time is also used somewhat as a de facto official time for all of the United States because it includes the capital city (Washington D.C.), the most populous city (New York City), and half of the country's population. For this reason, media organizations will often report when events happened or are scheduled to happen in Eastern Time even if they occurred in another time zone, and TV schedules are also almost always posted in Eastern Time. In the United States, all nationally televised morning programs (except Good Morning America Weekend Edition which some ABC affiliates on the east coast air on a tape-delay), some daytime talk shows, evening newscasts, most talent and awards shows, and any other nationally televised event that airs live on American television during prime time and on the weekends (such as sports television) are broadcast live in the Eastern Time Zone. Major professional sports leagues also post all game times in Eastern time, even if both teams are from the same time zone, outside of Eastern Time. For example, a game time between two teams from Pacific Time Zone will still be posted in Eastern time (for example, one may see "Seattle at Los Angeles" with "10:00 p.m." posted as the start time for the game, often without even clarifying the time is posted in Eastern time).

Most cable television and national broadcast networks advertise airing times in Eastern time. National broadcast networks (ABC, CBS, The CW, FOX, NBC) generally have two primary feeds, an eastern feed for Eastern and Central time zones, and a tape-delayed western feed for the Pacific Time Zone. The prime time is set on Eastern and Pacific at 8:00 p.m., with the Central time zone stations receiving the eastern feed at 7:00 p.m. local time. Mountain Time Zone stations receive a separate feed at 7:00 p.m. local time. As Arizona does not observe daylight saving time, during the summer months, it has its own feed at 7:00 p.m. local time. Cable channels with a separate western feed (such as HBO, whose western feed is called "HBOW") generally air the same programming as the eastern feed delayed by three hours. Other cable networks such as the Discovery family of networks repeat their prime time programming three hours later; this allows for the same show to be advertised as airing at "8:00 p.m. E/P" (that is, "8:00 p.m. Eastern and Pacific time"). Networks specializing in the airing of sports events, such as ESPN, advertise all of their programming in Eastern and Pacific, incorporating the three-hour time difference (as in "8:00 p.m. Eastern/5:00 p.m. Pacific") and leaving viewers in the remaining time zones to calculate start time in their own areas.

The Bahamas and Haiti officially observe both Eastern Standard Time during the winter months and Eastern Daylight Time during the summer months. Cuba generally follows the U.S. with Eastern Standard Time in the winter, and Eastern Daylight Time in the summer, but the exact day of change varies year to year. Cayman Islands and Jamaica use Eastern Standard Time year-round.

The Turks and Caicos Islands followed Eastern Time with daylight saving until 2015, when the territory switched to the Atlantic Time Zone. The Turks and Caicos Islands switched back to the pre-2015 schedule in March 2018.^[9] A 2017 consultation paper highlighted the advantage for business and tourism of being in the same time zone as the eastern United States as an important factor in the decision.^[10]

In Central America, the countries from Guatemala to Costa Rica use Central Standard Time UTC−06:00 year-round, but Panama uses Eastern Standard Time (UTC−05:00) year-round.

In South America, the state of Acre and the southwest part of the state of Amazonas (both in Brazil), along with Colombia, Ecuador (except for the Galápagos Islands, which use Central Standard Time), and Peru also use Eastern Standard Time year-round.