(CNN) -- Here's a look at what you need to know about Veterans Day, a holiday honoring men and women who have served in the U.S. armed forces.
Facts: Celebrated annually on November 11th, the anniversary of the end of World War I.
There are more than 21 million veterans in the U.S., according to the Census Bureau.
There are 1.6 million female veterans, as of 2011.
Approximately 42% of U.S. veterans are over the age of 65.
There are 1.8 million veterans of World War II still living.
Timeline: November 11, 1918 - The armistice ending World War I begins at 11 am.
1919 - President Woodrow Wilson proclaims November 11 as Armistice Day.
May 13, 1938 - Armistice Day becomes a federal holiday.
June 1, 1954 - President Eisenhower signs a bill changing Armistice Day to Veterans Day in order to include all U.S. veterans.
May 30, 1958 - Unknown Soldiers from World War II and the Korean War are reburied next to the Unknown Soldier from World War I.
1968 - Congress changes the date of Veterans Day to the fourth Monday in October in order to give federal employees a three-day weekend. The change begins in 1971.
September 25, 1975 - President Gerald Ford changes the date of Veterans Day back to November 11. The change begins in 1978.
May 28, 1984 - An unknown soldier from the Vietnam War is reburied in Arlington National Cemetery. In 1998, he is identified through DNA tests as Michael Blassie, a 24-year-old pilot shot down in 1972 on the border of Cambodia.