Preface of the special issue on the conference on Computer-Aided Verification 2020 and 2021

This special issue of the Journal on Formal Methods in System Design features extended and revised versions of select contributions presented at the Conference on Computer-Aided Verification (CAV) 2020 1,2 and 2021 3,4.CAV is an annual conference dedicated to the advancement of the theory and practice of computer-aided formal analysis methods for hardware and software systems.The primary focus of CAV is to extend the frontiers of verification techniques by expanding to new domains such as security, quantum computing, and machine learning.Due to the coronavirus disease (COVID-19) outbreak, both events took place online as virtual conferences.CAV 2020 was held as a virtual conference during July 21-24, 2020.The tutorial day was on July 20, 2020, and the pre-conference workshops were held during July 19-20, 2020.CAV 2021 was held as a virtual conference during July 20-23, 2021.The tutorial days were on July 19 and July 24, 2021, and the pre-conference workshops were held during July 18-19, 2021.This special issue contains the following 8 contributions, which are extended versions of the conference publications selected by the program committee among the top papers in their respective year.All the extended papers were reviewed by at least two experts in at least two rounds of peer-review:• Hashing-Based Approximate Counting of Minimal Unsatisfiable Subsets (CAV 2020 article 5) introduces an approximate counting algorithm to determine the number of minimal unsatisfiable subsets of a logic formula in conjunctive normal form.