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.