Static analysis allows us to determine aspects of the dynamic behavior of p- grams and systems without actually executing them. Traditionally used in - timizing compilers, static analysis is now also used extensively in veri?cation, software certi?cation and semantics-based manipulation. The research com- nity in static analysis covers a broad spectrum from foundational issues - new semantic models of programming languages and systems - through to practical tools.TheseriesofStatic AnalysisSymposia hasservedasthe primaryvenue for presentation and discussion of theoretical, practical and application advances in the area. This volume contains the papers accepted for presentation at the 12th Int- national Static Analysis Symposium (SAS 2005) which was held 7-9 September 2005 at Imperial College London. A total of 66 papers were submitted; the Program Committee held an online discussion which led to the selection of 22 papers for presentation. The selection was based on scienti?c quality, originality and relevance to the scope of SAS. Every paper was reviewed by at least 3 PC members or external referees. This volume also includes abstracts of talks given by the two invited speakers: Samson Abramsky FRS (University of Oxford) and Andrew Gordon (Microsoft Research, Cambridge). OnbehalfoftheProgramCommittee, theProgramChairwouldliketothank all of the authors who submitted papers and all of the external referees for their careful work in the reviewing process. The Program Chair would also parti- larly like to thank Igor Siveroni who provided local support for the conference management system and who helped in organizing the structure of this volume.