The International Conference on Rigorous State-based Methods (ABZ 2020) is an international forum for the cross-fertilization of related state-based and machine-based formal methods, mainly Abstract State Machines (ASM), Alloy, B, TLA+, VDM and Z. Rigorous state-based methods share common conceptual foundation and are widely used in both academia and industry for the design and analysis of hardware and software systems. The name ABZ was invented at the first conference held in London in 2008, where the ASM, B and Z conference series merged into a single event. The second ABZ 2010 conference was held in Orford (Canada), where the Alloy community joined the event; ABZ 2012 was held in Pisa (Italy), which saw the inclusion of the VDM community (but not in the title); ABZ 2014 was held in Toulouse (France), which brought the inclusion of the TLA+ community into the ABZ conference series. Lastly, ABZ 2016 conference was held in Linz, Austria and ABZ 2018 in Southampton, UK. In 2018 the steering committee decided to retain the (well-known) acronym ABZ and add the subtitle ``International Conference on Rigorous State-Based Methods'' to make more explicit the intention to include all state-based formal methods. Started 2014 in Toulouse, each ABZ asked for the application of formal specifications on industrial case studies. This year, we extend the previous areas (aerospace, medical equipment, rails) with the automotive domain. A specification of an adaptive light and speed control system similar to the available real systems was provided by Frank Houdek, who also answered almost a hundred questions and gave clarifying explanations, for which we would like to thank him. The objective of these case studies is to provide an opportunity to demonstrate the applicability of the ABZ methods to real examples and also to allow a better comparison of the them. ABZ 2020 received 55 submissions from 21 countries around the world. The selection process was rigorous, where each paper received at least three reviews. The program committee, after careful discussions, decided to accept 12 full research papers, 6 case study papers and 9 short research papers. One extended abstract of one of the keynote speakers and one invited research paper are also included in the proceedings. All accepted papers cover broad research areas on both theoretical, systems and practical aspects of state-based methods. For the first time in ABZ series, in 2020 a doctoral symposium is organized and PhD students had to submit a short paper presenting their PhD topics; those 6 submissions have been evaluated by a separate PC committee including the two chairs of ABZ. The conference was to be held on May 27-29, 2020 in Ulm, Germany, but due to the historical crisis caused by the corona virus with an unprecedented international lock-down, travel-restrictions, and sadly many deaths around the world, we had to cancel the conference and postpone it to next year 2021. At ABZ 2021, all authors of accepted papers of ABZ 2020 are requested to present their research in addition to the new accepted papers. We are honored that all three distinguished guests as keynote speakers have agreed to give their keynotes next year: Ana Cavalcanti, University of York, York, UK, will give a talk entitled ``RoStar technology --- a roboticist's toolbox for combined proof and sound simulation''; Uwe Glässer, Simon Fraser University, Vancouver, CA, will give a talk entitled ``Quantifying Uncertainty in ASM Models with Markov Processes'' and Gilles Dowek, INRIA/ENS Paris-Saclay, France. The EasyChair conference management system was set up for ABZ 2020, supporting submission, review and volume edition processes. We acknowledge it is an outstanding tool for the academic community. We would like to thank all the authors who submitted their work to ABZ 2020. We are grateful to the program committee members and external reviewers for their high-quality reviews and discussions. Finally, we wish to thank the Organizing Committee members for their continuous support. We hope the corona crisis will be over within the next weeks or months and that the enormous economic consequences of this crisis will be outweighed by more humanity in the world. We are looking forward to welcoming many conference attendants in Ulm next year and hope they will enjoy the technical program, informal meetings, and interactions with colleagues from all over the world; and of course, we are confident they will like the city of Ulm, Germany. For readers of these proceedings, we hope these papers are interesting and they inspire ideas for future research.