This book constitutes the thoroughly refereed post-conference proceedings of the 18th International Symposium on Logic-Based Program Synthesis and Transformation, LOPSTR 2008, held in Valencia, Spain, during July 17-18, 2008. The 11 revised full papers presented together with one invited talk were carefully reviewed and selected for inclusion in the book. LOPSTR traditionally solicits papers in the areas of specification, synthesis, verification, transformation, analysis, optimization, composition, security, reuse, applications and tools, component-based software development, software architectures, agent-based software development, and program refinement.