Twenty-second Amendment to the United States Constitution
The Twenty-second Amendment (Amendment XXII) to the United States Constitution sets a limit on the number of times an individual is eligible for election to the office of President of the United States, and also sets additional eligibility conditions for presidents who succeed to the unexpired terms of their predecessors.
List of Presidents of the United States by time in office
William Henry Harrison spent the shortest time in office, and Franklin D. Roosevelt spent the longest. Roosevelt is the only president to have served more than two terms. Following ratification of the Twenty-second Amendment in 1951, presidents—beginning with Dwight D. Eisenhower—have been ineligible for election to a third term or for election to a second full term after serving more than two years of a term to which some other person was elected president. The amendment contained a grandfather clause that explicitly exempted the incumbent president, then Harry S. Truman, from the new term limitations, which first applied to Dwight D. Eisenhower.