Daylight Saving Time (DST) begins at 2am on Sunday, Mar. 11, 2018 with "spring forward" when most of the United States moved clocks forward by one hour, and will end at 2am on Sunday, Nov. 4, 2018 when those clocks will "fall back" one hour.

DST was implemented in the United States nationally on Mar. 31, 1918 as a wartime effort to save an hour's worth of fuel (gas or oil) each day to light lamps and coal to heat homes. It was repealed nationwide in 1919, and then maintained by some individual localities (such as New York City) in what Time Magazine called "a chaos of clocks" until 1966 when the Uniform Time Act made DST consistent nationwide.

Approximately 1.5 billion people in 70 countries observe DST worldwide. In the United States, 48 states participate in Daylight Saving Time. Arizona, Hawaii, some Amish communities, and the American territories (American Samoa, Guam, Puerto Rico, the Virgin Islands, and the Northern Mariana Islands) do not observe DST. In the first quarter of 2018, bills were considered in at least 13 state legislatures to amend DST or exempt individual states from DST. 33% of Americans think DST is worth the effort, while 48% do not and 19% are not sure.

People in favor of keeping Daylight Saving Time say it allows drivers to commute more safely in daylight, promotes outdoor activities, and stimulates the economy. Those who oppose Daylight Saving Time say that the change is a harmful disruption to health and work productivity, and is expensive. While the time change was initially implemented to save energy, studies are mixed and have found our current use of air conditioning and heating may negate the energy saved by not having to use electric lights and may actually increase electricity usage.