Constitutes the refereed proceedings of the 6th International Symposium on Frontiers of Combining Systems, FroCoS 2007, held in Liverpool, UK, September 10-12, 2007. This book presents 14 revised full papers that were reviewed and selected.

Section 1. Invited Contributions.- Architecting Solvers for SAT Modulo Theories: Nelson-Oppen with DPLL.- From KSAT to Delayed Theory Combination: Exploiting DPLL Outside the SAT Domain.- Hierarchical and Modular Reasoning in Complex Theories: The Case of Local Theory Extensions.- Temporalising Logics: Fifteen Years After.- Section 2. Technical Papers.- Termination of Innermost Context-Sensitive Rewriting Using Dependency Pairs.- A Compressing Translation from Propositional Resolution to Natural Deduction.- Combining Algorithms for Deciding Knowledge in Security Protocols.- Combining Classical and Intuitionistic Implications.- Towards an Automatic Analysis of Web Service Security.- Certification of Automated Termination Proofs.- Temporal Logic with Capacity Constraints.- Idempotent Transductions for Modal Logics.- A Temporal Logic of Robustness.- Noetherianity and Combination Problems.- Languages Modulo Normalization.- Combining Proof-Producing Decision Procedures.- Visibly Pushdown Languages and Term Rewriting.- Proving Termination Using Recursive Path Orders and SAT Solving.