This book constitutes the refereed proceedings of the 6th International Symposium on Frontiers of Combining Systems, FroCoS 2007, held in Liverpool, UK, September 10-12, 2007.

The 14 revised full papers presented were carefully reviewed and selected. The papers are organized in topical sections on combinations of logics, theories, and decision procedures; constraint solving and programming; combination issues in rewriting and programming as well as in logical frameworks and theorem proving systems.