The crossing number of K11 is 100

The crossing number of Kn is known for n ⩽ 10. We develop several simple counting properties that we shall exploit in showing by computer that cr(K11 = 100, which implies that cr(K12) = 150. We also determine the numbers of non-isomorphic optimal drawings of K9 and K10. © 2007 Wiley Periodicals, Inc. J Graph Theory 56: 128–134, 2007