Gettysburg is perhaps the most written-about battle in American history, so any attempt to put together a complete bibliography of books related to the battle would be doomed from the start. What follows is a list of sources used by Steve Schmidt to produce the chronologies, supplemented by some books that the publisher (Jim Epperson) thinks are good sources.
Boatner, Mark, Civil War Dictionary; Random House, 1959.
Catton, Bruce,. Glory Road; Doubleday, 1952.
Clark, Champ, Gettysburg: The Confederate High Tide; Time-Life Books, 1985.
Coddington, Edwin, The Gettysburg Campaign: A Study in Command; Scribner, 1968.
Dyer, Frederick, A Compendium of the War of the Rebellion; Yoseloff, 1909.
Foote, Shelby, The Civil War: A Narrative; Fredricksburg to Meridian; Random House, 1963.
Luvaas, Jay, and Nelson, Harold W., The U.S. War College Guide to the Battle of Gettysburg, South Mountain Press, 1986
Mosby, Jonathan S, Stuarts Cavalry in the Gettysburg Campaign; Moffet, Yard, and Co, 1907.
Pfanz, Harry W, Gettysburg: The Second Day; UNC Press, 1987
Pfanz, Harry W, Gettysburg: Culps Hill and Cemetery Hill; UNC Press, 1993.
Stewart, George, Pickett's Charge: A Microhistory of the Final Attack at Gettysburg, Houghton-Mifflin, 1959.
Tucker, Glenn, High Tide at Gettysburg, Morningside Press, 1973.
Zimmermann, Richard J, Unit Organizations of the Civil War; Rafm, 1982.
The relevant volume of the Official Records is Vol. XXVII (three parts), corresponding to serial volumes 43, 44, and 45.
In addition, Vol. 3 of Battles and Leaders contains the Gettysburg material, and numerous biographies and unit histories will shed some light on this battle.