Today is Constitution Day.
Here are some history books (and one primary source) on the Constitution that I have found helpful:
Richard Beeman, Plain, Honest Men: The Making of the American Constitution
Pauline Maier, The People Debate the Constitution, 1787-1788
Gordon Wood, The Creation of the American Republic
Akhil Amar, America’s Constitution: A Biography
Woody Holton, Unruly Americans and the Origins of the Constitution