The abstracts and papers in this volume were presented at the Fifth Annual International Computing and Combinatorics Conference (COCOON ’99), which was held in Tokyo, Japan from July 26 to 28, 1999. The topics cover most aspects of theoretical computer science and combinatorics pertaining to computing. In response to the call for papers, 88 high-quality extended abstracts were submitted internationally, of which 46 were selected for presentation by the p- gram committee. Every submitted paper was reviewed by at least three program committee members. Many of these papers represent reports on continuing - search, and it is expected that most of them will appear in a more polished and complete form in scienti c journals. In addition to the regular papers, this v- ume contains abstracts of two invited plenary talks by Prabhakar Raghavan and Seinosuke Toda. The conference also included a special talk by Kurt Mehlhorn on LEDA (Library of E cient Data types and Algorithms). The Hao Wang Award (inaugurated at COCOON ’97) is given to honor the paper judged by the program committee to have the greatest scienti c merit. The recipients of the Hao Wang Award 1999 were Hiroshi Nagamochi and Tos- hide Ibaraki for their paper An Approximation for Finding a Smallest 2-Edge- Connected Subgraph Containing a Speci ed Spanning Tree".