Pre-proceedings of the 31st International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2021)

This volume constitutes the pre-proceedings of the 31st International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2021), held on 7-8th September 2021 as a hybrid (blended) meeting, both in-person (at the Teachers' House in Tallinn, Estonia) and virtual, and co-located with the 23rd International Symposium on Principles and Practice of Declarative Programming (PPDP 2021). After discussion at the symposium papers will go through a second round of refereeing and selection for the formal proceedings.