This book constitutes the proceedings of the 20th International Conference on Relational and Algebraic Methods in Computer Science, RAMiCS 2023, which took place in Augsburg, Germany, during April 3–6, 2023.The 17 papers presented in this book were carefully reviewed and selected from 26 submissions.They deal with the development and dissemination of relation algebras, Kleene algebras, and similar algebraic formalisms. Topics covered range from mathematical foundations to applications as conceptual and methodological tools in computer science and beyond.Apart from the submitted articles, this volume features the abstracts of the presentations of the three invited speakers.