This book constitutes the refereed proceedings of the 33rd International Symposium on Logic-Based Program Synthesis and Transformation, LOPSTR 2023, held in Cascais, Portugal, during October 23-24, 2023. The 8 full papers and 4 short papers included in this book were carefully reviewed and selected from 29 submissions.

K​eynotes.- Unification modulo equational theories in languages with binding operators.- Horn Clauses Analysis, Transformation and Synthesis.- Design Datalog Templates for Synthesizing Bidirectional Programs from Tabular Examples.- Transforming big-step to small-step semantics using interpreter specialisation.- Constrained Horn Clauses Satisfiability via Catamorphic Abstractions.- Static analysis and Type systems.- A reusable machine-calculus for automated resource analyses.- Approach for Designing and Composing Abstract Domains.- A Logical Interpretation of Asynchronous Multiparty Compatibility.- Relational Solver for Java Generics Type System.- Unification and substitution in (C)LP.- Predicate Anti-unification in (Constraint) Logic Programming.- A term matching algorithm and substitution generality.- Knowledge representation and AI-based learning.- A novel EGs-based framework forsystematic propositional-formula simplification.- From Static to Dynamic Access Control Policies via Attribute-Based Category Mining.- Towards a Certified Proof Checker for Deep Neural Network Verification.