This volume of the Lecture Notes in Computer Science series contains all papers accepted for presentation at the 20th IFIP/IEEE International Workshop on Distributed Systems: Operations and Management (DSOM 2009), which was held in Venice, Italy, during October 27-28, 2009. DSOM 2009 was the 20th event in a series of annual workshops. It followed in the footsteps of previous successful meetings, the most recent of which were held on Samos, Greece (DSOM 2008), San Jos e, California, USA (DSOM 2007), Dublin, Ireland (DSOM 2006), Barcelona, Spain (DSOM 2005), and Davis, C- ifornia, USA (DSOM 2004). The goal of the DSOM workshops is to bring - gether researchersfromindustry andacademia workingin the areasofnetworks, systems, and service management, to discuss recent advances and foster future growth. In contrast to the larger management conferences, such as IM (Inter- tional Symposium on Integrated Network Management) and NOMS (Network OperationsandManagementSymposium),DSOMworkshopshaveasingle-track program in order to stimulate more intense interaction among participants.