This book constitutes the thoroughly refereed post-proceedings of the 9th International Workshop on Logic-Based Program Synthesis and Transformation, LOPSTR'99, held in Venice, Italy, in September 1999. The 14 revised full papers presented together with an invited paper and 2 tutorial lectures have gone through two rounds of reviewing and revisions. The book is divided into topical sections on software development, analysis and specialization, transformation, and verification.