This book constitutes the refereed proceedings of the 31st International Conference on Logic-Based Program Synthesis and Transformation, LOPSTR 2021, which was held during September 7-8, 2021.*
The 8 papers presented in this volume were carefully reviewed and selected from a total of 15 reviewed submissions. Additionally, the book also contains 1 full-length invited talk.
*Conference was held as a hybrid event due to the COVID-19 pandemic.

String Abstract Domains and Their Combination. - Data Type Inference for Logic Programming.- Automating the Functional Correspondence between Higher-Order Evaluators and Abstract Machines.- S-semantics - an Example.- Disjunctive Delimited Control.- Towards Substructural Property-Based Testing.- The Next 700 Program Transformers.- Representation and Processing of Instantaneous and Durative Temporal Phenomena.- Pre x-Based Tracing in Message-Passing Concurrency.