This book is based on the proceedings of the Colloquium on Mathematics and Computer Science held in the University of Versailles-St-Quentin on September 18- It contains articles on topics that are relevant both to Mathematics and 20, 2000. to Computer Science. These articles have been selected throughout a rigourous process; each of them has been submitted to two referees at least. This selection process, which took place under the supervision of the scientific committee, en­ sures the high level and the originality of the contributions. We thank the invited speakers, the authors, the participants to the collo­ quium and, of course, the Scientific Committee whose members were D. Aldous, F. Baccelli, P. Cartier, B. Chauvin, P. Flajolet, J.M. Fourneau, D. Gardy, D. Gouyou­ Beauchamps, R. Kenyon, J.F. Le Gall, C. Lemarechal, R. Lyons, A. Mokkadem, A. Rouault and C. Roucairol. We also take this opportunity to thank the University of Versailles-St-Quentin, the University of Paris-Sud (Orsay) and the Centre National de la Recherche Sci­ entifique (CNRS), whose financial and material support contributed to the success of the Colloquium.