Daylight Saving Time begins again Sunday morning (March 13, 2016) at 2:00 a.m. when clocks "spring forward" one hour to 3:00 a.m. and an hour's sleep is lost.
Most current computers, cell phones and other digital devices will make the adjustment automatically, though other devices will need to be reset manually - and the occasional technology glitch leads to clocks that are reset on the wrong day, or not at all.
Prior to the Uniform Time Act of 1966, each state determined its own start and end dates for Daylight Saving Time (DST) - and even which parts of the state would use the system.
With the advent of the Time Act, a national standard was applied that specified the start of DST as the last Sunday in April, continuing through the last Sunday in October. The law was amended in 1986 to move the start date to the first Sunday in April.
The Energy Policy Act of 2005 further amended the start of DST to the second Sunday in March and the end to the first Sunday in November. Implementation began in 2007.
Despite the laws setting national standards, states can exempt themselves from DST under certain circumstances. Currently, Arizona and Hawaii do not observed DST.
While Daylight Saving Time was intended to be an energy saving tool that reduced the need for lighting - originally the primary use of electricity - a report released by the Department of Energy in 2008 showed a reduction of just 0.03% in electrical use in 2007.