Bibliography of the Writings of Clarence Irving Lewis: A definitive list, from the Pragmatism Cybrary.
Biography.com: Lewis, Clarence Irving: Concise biographical paragraph.
Clarence Irving Lewis: A scholarly treatment of this pragmatist thinker, by Eric Dayton. From the Internet Encyclopedia of Philosophy.
Lewis, Clarence Irving: Short entry from the 2001 Columbia Encyclopedia.
Terry Peterson's Essays: Three essays to facilitate the understanding of C.I. Lewis's thought. Includes a page-by-page annotation of Mind and the World Order.