Starting in 2007, daylight time begins in the United States on the second Sunday in March and ends on the first Sunday in November. On the second Sunday in March, clocks are set ahead one hour at 2:00 a.m. local standard time, which becomes 3:00 a.m. local daylight time. On the first Sunday in November, clocks are set back one hour at 2:00 a.m. local daylight time, which becomes 1:00 a.m. local standard time. These dates were established by Congress in the Energy Policy Act of 2005, Pub. L. no. 109-58, 119 Stat 594 (2005).
Not all places in the U.S. observe daylight time. In particular, Hawaii and most of Arizona do not use it. Indiana adopted its use beginning in 2006.
In 2006, daylight time begins on April 2 and ends on October 29.
In 2007, daylight time begins on March 11 and ends on November 4. [New law goes into effect.]
In 2008, daylight time begins on March 9 and ends on November 2.
In 2009, daylight time begins on March 8 and ends on November 1.
Many other countries observe some form of "summer time", but they do not necessarily change their clocks on the same dates as the U.S.
Daylight time and time zones in the U.S. are defined in the U.S. Code, Title 15, Chapter 6, Subchapter IX - Standard Time.
