This book constitutes the refereed proceedings of the 12th International Conference on
Foundations of Software Science and Computational Structures FOSSACS 2009 held in York UK
in March 2009 as part of ETAPS 2009 the European Joint Conferences on Theory and Practice of
Software. The 30 revised full papers presented together with two invited talks were carefully
reviewed and selected from 102 full paper submissions. The topics addressed are semantics
logics and automata algebras automata theory processes and models security probabilistic
and quantitative models synthesis and program analysis and semantics.
