Want to know where DST comes from?
The main purpose of Daylight Saving Time (called "Summer Time" many places in the world) is to make better use of daylight.
Daylight Saving Time also saves energy.
There is a small public health benefit to Daylight Saving time.
Early laws in Britain
A bill was drafted in 1909 and introduced in Parliament several times, but it met with ridicule and opposition, especially from farming interests. Generally lampooned at the time, Willett died in 1915, but a year later Daylight Saving Time (Summer Time) was adopted in England in May 1916, following the lead of Germany. The motivation was to conserve coal. There was a fair bit of opposition from agricultural interests who wanted daylight in the morning, but Lord Balfour came forward with a unique concern.
His campaign led to the introduction of British Summer Time in an Act of Parliament in 1916. Clocks were put one hour ahead of Greenwich Mean Time (GMT) during the Summer months. The energy saving benefits of this were recognized during World War II, when clocks were put two hours ahead of GMT during the Summer. This became known as Double Summer Time. During the war, clocks remained one hour ahead of GMT throughout the winter.
Early adoption and U.S. law
Daylight saving has been used in the United States and in many European countries since World War I, when the system was adopted in order to conserve fuel needed to produce electric power. In 1918, in order to conserve resources for the war effort, Congress placed the country on Daylight Saving Time for the remainder of WW I. It was observed for seven months in 1918 and 1919. The law, however, proved so unpopular (mostly because people rose earlier and went to bed earlier than we do today) that the law was later repealed in 1919 over President Wilson's veto. It was continued in a few states (Massachusetts, Rhode Island) and some cities (New York, Philadelphia, Chicago, and others).
During World War II, the United States observed year-round Daylight Saving Time (from February 2nd, 1942 to September 30th, 1945). From 1945 to 1966, there was no federal law about Daylight Saving Time. So, states and localities were free whether to observe or not to observe Daylight Saving Time and could choose when it began and ended. This, however, caused confusion -- especially for the broadcasting industry, and for railways, airlines, and bus companies. Because of the different local customs and laws, radio and TV stations and the transportation companies had to publish new schedules every time a state or town began or ended Daylight Saving Time.
Daylight Saving Time, for the U.S. and its territories, is NOT observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, the Eastern Time Zone portion of the State of Indiana, and the state of Arizona (not the Navajo Indian Reservation, which does observe). Navajo Nation participates in the Daylight Saving Time policy, due to its large size and location in three states.

May 2003 June 2003 July 2003 August 2003 September 2003 November 2003 December 2003 January 2004 February 2004 March 2004 April 2004 May 2004 June 2004 July 2004 August 2004 September 2004 November 2004 December 2004 February 2005 March 2005 April 2005 May 2005 June 2005 July 2005 August 2005 September 2005 October 2005 November 2005 December 2005 January 2006 February 2006 March 2006 April 2006 May 2006 June 2006 July 2006 August 2006 September 2006 October 2006 November 2006 December 2006 January 2007 February 2007 March 2007 April 2007 May 2007 June 2007 July 2007 August 2007 September 2007 October 2007 November 2007 December 2007 January 2008 February 2008 March 2008 April 2008 May 2008 June 2008 July 2008 August 2008 September 2008 October 2008 November 2008 December 2008 January 2009 February 2009