Combinatorial Algorithms

The 20th InternationalWorkshop on CombinatorialAlgorithms was held during June 28 - July 2, 2009 in the picturesque castle of Hradec nad Moravic´ ?,located in the north-east corner of the Czech Republic. IWOCA - the workshopthat originated19 yearsagoas AWOCA- madea big step towards globalization this year. After 19 conferences held in Australia, Indonesia, Korea,and Japan, the 20th anniversarywas celebrated by taking the conference outside the Australasian region for the ?rst time. Another novelty this year was that the proceedings are being published by Springer in the LNCS series. Our Call for Papers brought an overwhelming response of the combinatorial community. IWOCA 2009 received over 100 submissions, more than twice the amount it received before. Most of the submissions were of exceptionally high quality and thus the Program Committee was faced with hard work and so- times hard decisions. Many very good papers had to be rejected because of the limitedcapacityoftheconferenceschedule.In the end,41contributedtalkswere presented during the conference - the maximum number that we could ?t in the program. We would like to thank all who sent their submissions and to congratulate all the authors of the accepted papers. They contributed to what was a most successful conference. We also thank all the authors who submitted posters for the poster session (not included in the proceedings).