Daylight savings time had been theorized as early as the days of Ben Franklin, but wasn't widely adopted until WWI.
During World War I, DST was first adopted in Germany, which was quickly followed by Britain and countries on both sides, and eventually, America. Daylight replaced artificial lighting and saved precious fuel for the war effort.
After the war American farmers fought and defeated urban dwellers and President Woodrow Wilson and got DST repealed, returning the country to "God's Time.” Spotty and inconsistent use of daylight saving time in the United States and around the world caused problems, unusual incidents and, occasionally, tragedies. For example, disregard of a change to DST caused a major train wreck in France, killing two and injuring many.
During WWII, DST was adopted again but this time permanently. All combatants on both sides quickly adopted DST to save vital energy resources for the War. The U.S. enacted FDR's year-round DST law just 40 days after Pearl Harbor.
As part of the Energy Policy Act of 2005, the U.S. DST period was extended by three weeks in the spring and one week in the fall, commencing 2007.
Currently, the entire country observes this DST period except for: Arizona, Hawaii, the Eastern time zone portion of Indiana, and the U. S. insular areas of Puerto Rico, the U. S. Virgin Islands, American Samoa, and Guam--all of which have chosen to stay on standard time all year.
In 2005, Indiana, which has long been a continuing hotbed of DST controversy, passed a law adopting statewide daylight saving time, starting in 2006.
For 2006, the DST period is from Sunday April 2 to Sunday October 29.
For 2007, the DST period is from Sunday March 11 to Sunday November 4.