- David Brooks: “Math Pioneers: Proving the four-color theorem expanded math's frontiers”, article in University of New Hampshire Magazine
- Dennis Overbye: “Kenneth I. Appel, Mathematician Who Harnessed Computer Power, Dies at 80”, article in The New York Times
- Kenneth Ira Appel at the Mathematics Genealogy Project
- Biography of Kenneth Ira Appel at MacTutor History of Mathematics
- Biography of Kenneth Ira Appel at Wikipedia
