This book constitutes the refereed proceedings of the 6th International Conference on Foundations of Software Science and Computation Structures, FOSSACS 2003, held in Warsaw, Poland in April 2003.

The 26 revised full papers presented together with an invited paper were carefully reviewed and selected  from 96 submissions. Among the topics covered are algebraic models; automata and language theory; behavioral equivalences; categorical models; computation processes over discrete and continuous data; computation structures; logics of programs; models of concurrent, reactive, distributed, and mobile systems; process algebras and calculi; semantics of programming languages; software specification and refinement; transition systems; and type systems and type theory.