Thisvolumecontainsthe30regularpapers, the11shortpapersandtheabstracts oftwoinvited keynotesthatwerepresentedatthe12thInternationalConference on Principles of Distributed Systems (OPODIS) held during December 15 18, 2008 in Luxor, Egypt. OPODIS is a yearly selective international forum for researchers and prac- tioners in design and development of distributed systems. This year, we received 102 submissions from 28 countries. Each submission was carefully reviewed by three to six Program Committee members with the help of external reviewers, with 30 regular papers and 11 short papers being...