This book constitutes the refereed proceedings of the 30thInternational Conference on Logic-Based Program Synthesis and Transformation, LOPSTR 2020, which was held during September 7-9, 2020.The 15 papers presented in this volume were carefully reviewed and selected from a total of 31 submissions. The book also contains two invited talks in full paper length. The contributions were organized in topical sections named: rewriting; unification; types; verification; model checking and probabilistic programming; program analysis and testing; and logics.