Memorial Day is a United States Federal Holiday that is observed on the last Monday of May (observed in 2008 on May 26). It was formerly known as Decoration Day; and for many years observed on May 30, regardless of the day of the week. This holiday commemorates U.S. men and women who have died in military service to their country. It began first to honor Union soldiers who died during the American Civil War. After World War I, it was expanded to include those who died in any war or military action.