This book constitutes the thoroughly refereed postproceedings of the 13th International Symposium on Logic Based Program Synthesis and Transformation, LOPSTR 2003, held in Uppsala, Sweden in August 2003. rounds of reviewing and revision from 32 submissions. Also included are an invited paper and abstracts of 5 papers presented at the workshop. The papers are organized in topical sections on specification and synthesis, verification, analysis, transformation and specialization, and constraints.