This volume contains the 70 contributed papers and abstracts of two invited l- tures presented at the 12th Annual European Symposium on Algorithms (ESA 2004), held in Bergen, Norway, September 14 17, 2004. The papers in each s- tion of the proceedings are arranged alphabetically. The three distinguished - vited speakers were David Eppstein, Michael Fellows and Monika Henzinger. As in the last two years, ESA had two tracks, with separate program c- mittees, which dealt respectively with: the design and mathematical analysis of algorithms (the Design and A- lysis track); real-world...