This volume contains the proceedings of the 6th Symposium on Abstraction, Reformulation and Approximation (SARA 2005). The symposium was held at Airth Castle, Scotland, UK, from July 26th to 29th, 2005, just prior to the IJCAI 2005 conference in Edinburgh. Previous SARA symposia took place at JacksonHole in Wyoming, USA (1994),Ville d'Estrel in Qubec, Canada (1995), Asilomar in California, USA (1998), Horseshoe Bay, Texas, USA (2000), and Kananaskis, Alberta, Canada (2002). This was then the ?rst time that the s- posium was held in Europe. Continuing the tradition started with SARA 2000, the proceedings have been published in the LNAI series of Springer. Abstractions, reformulations and approximations (AR&A) have found app- cationsin avarietyofdisciplines andproblems,including constraintsatisfaction, design, diagnosis, machine learning, planning, qualitative reasoning, scheduling, resource allocation and theorem proving, but are also deeply rooted in philo- phy and cognitive science. The papers in this volume capture a cross-section of the various facets of the ?eld and of its applications. One of the primary uses of AR&A is oriented to overcome computational intractability.
AR&A techniques, however, have also proved useful for knowledge acquisition, explanation and other applications, as papers in this volume also illustrate.