The Workshop on Quantitative Logics (QUANTLOG 2009) will take place in Rhodes, Greece, July 11, 2009 as a satellite event of the 36th International Colloquium on Automata, Languages and Programming (ICALP 2009). It is organized under the auspices of the Department of Mathematics of the Aristotle University of Thessaloniki. The aim of the workshop is to provide a forum for researchers interested in the topic of quantitative logics to present their new results and to combine their efforts in the further development of the topic, with emphasis to its connection with automata theory as well as to practical applications.