Randomness Paul Vitányi Abstract: This is a draft of the chapter ``Randomness'' in 20th Century Mathematics prepared for the `Matematica, Logica, Informatica' Volume 12 of the Storia del XX Secolo, to be published by the Instituto della Enciclopedia Italiana. Excerpts of this draft appeared earlier in P.M.B. Vitanyi, ``Randomness''. In A. Schrijver, N. Temme, and K.R. Apt, Eds., From Universal morphisms to megabytes: a Baayen space Odyssey, pages 627--642 CWI, Amsterdam, 1994. We present in a single essay a combination and completion of the several aspects of the problem of randomness of individual objects which of necessity occur scattered in our text.