Invited Talk -- On Finite Alphabets and Infinite Bases II: Completed and Ready Simulation -- Mobile Processes -- A Theory for Observational Fault Tolerance -- Smooth Orchestrators -- On the Relative Expressive Power of Asynchronous Communication Primitives -- More on Bisimulations for Higher Order ?-Calculus -- Software Science -- Register Allocation After Classical SSA Elimination is NP-Complete -- A Logic of Reachable Patterns in Linked Data-Structures -- Distributed Computation -- Dynamic Policy Discovery with Remote Attestation -- Distributed Unfolding of Petri Nets -- On the ?-Calculus Augmented with Sabotage -- Categorical Models -- A Finite Model Construction for Coalgebraic Modal Logic -- Presenting Functors by Operations and Equations -- Bigraphical Models of Context-Aware Systems -- Processes for Adhesive Rewriting Systems -- Real Time and Hybrid Systems -- On Metric Temporal Logic and Faulty Turing Machines -- Denotational Semantics of Hybrid Automata -- Process Calculi -- Reversing Algebraic Process Calculi -- Conjunction on Processes: Full-Abstraction Via Ready-Tree Semantics -- Undecidability Results for Bisimilarity on Prefix Rewrite Systems -- Automata and Logic -- Propositional Dynamic Logic with Recursive Programs -- A Semantic Approach to Interpolation -- First-Order and Counting Theories of ?-Automatic Structures -- Parity Games Played on Transition Graphs of One-Counter Processes -- Domains, Lambda Calculus, Types -- Bidomains and Full Abstraction for Countable Nondeterminism -- An Operational Characterization of Strong Normalization -- On the Confluence of ?-Calculus with Conditional Rewriting -- Security -- Guessing Attacks and the Computational Soundness of Static Equivalence -- Handling exp,× (and Timestamps) in Protocol Analysis -- Symbolic and Cryptographic Analysis ofthe Secure WS-ReliableMessaging Scenario.

This book constitutes the refereed proceedings of the 9th International Conference on Foundations of Software Science and Computation Structures, FOSSACS 2006, held in Vienna, Austria in March 2006 as part of ETAPS. The 28 revised full papers presented together with 1 invited paper were carefully reviewed and selected from 107 submissions. The papers are organized in topical sections on mobile processes, software science, distributed computation, categorical models, real time and hybrid systems, process calculi, automata and logic, domains, lambda calculus, types, and security.