This volume constitutes the thoroughly refereed post-conference proceedings of the 19th International Symposium on Logic-Based Program Synthesis and Transformation, LOPSTR 2009, held in Coimbra, Portugal, during September 9-11, 2009. The 14 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.