The aim of the LOPSTR series is to stimulate and promote international research and collaboration on logic-based program development. LOPSTR is open to contributions in logic-based program development in any language paradigm. LOPSTR has a reputation for being a lively, friendly forum for presenting and discussing work in progress. Formal proceedings are produced only after the symposium so that authors can incorporate this feedback in the published papers. The 23rd International Symposium on Logic-based Program Synthesis and Transformation (LOPSTR 2013) will be held in Madrid, Spain; previous symposia were held in Leuven, Odense, Hagenberg, Coimbra, Valencia, Lyngby, Venice, London, Verona, Uppsala, Madrid, Paphos, London, Venice, Manchester, Leuven, Stockholm, Arnhem, Pisa, Louvain-la-Neuve and Manchester (you might have a look at the contents of past LOPSTR symposia). LOPSTR 2013 will be co-located with PPDP 2013 (International ACM SIGPLAN Symposium on Principles and Practice of Declarative Programming).