Proceedings of the 20th edition of the BElgian-NEtherlands software eVOLution symposium Gemma Catolino1 , Dario Di Nucci1 and Damian A. Tamburri2 1 Tilburg University, Jheronimus Academy of Data Science, Netherlands 2 Eindhoven University of Technology, Jheronimus Academy of Data Science, Netherlands The goal of BENEVOL is to bring together researchers who are working in the field of software evolution and maintenance, with a focus on the current state of the art and practice emerging in the Belgian-Netherlands technical knowledge and research communities. BENEVOL offers an informal forum to meet and discuss new ideas, important problems, and obtained research results. While originally planned as a physical event, the 20th edition of BENEVOL was organized by the Jheronimus Academy of Data Science in Den Bosch (NL) and hosted online from 07 to 08 December 2021. Us the program chairs accepted 9 techni- cal papers and 13 presentation abstracts which reflected the expected quality of technical content. Technical papers underwent a mild yet constructive review. We explicitly solicited papers in the early stages of research, which are still rather rough around the edges and could benefit from feedback from the community. Technical papers were reviewed by at least three program committee members, assessing whether they are within the scope of BENEVOL (i.e., software maintenance and evolution) and meet its quality criteria. The papers part of the proceedings includes the feedback received during the workshop. Presentation abstracts report on research results that have already been published or are ready to be submitted to a conference or a journal. They were reviewed for relevance and are not included in the BENEVOL proceedings but are available on the website of the workshop. BENEVOL 2021 featured one keynote: Vladimir Kovalenko, the Intelligent Collaboration Tools Lab leader at JetBrains Research in Amsterdam, made a case for collaboration tools as a fertile ground for data-driven enhancement and discussed several related challenges. We thank our program committee members for producing outstanding reviews and all the attendees for the feedback and good discussions taking place online. Everyone took a diligent stand in aiding all with fruitful comments and remarks: we are thankful for such contributions. BENEVOL’21: The 20th Belgium-Netherlands Software Evolution Workshop, December 07–08, 2021, ’s-Hertogenbosch (virtual), NL Envelope-Open g.catolino@tilburguniversity.edu (G. Catolino); d.dinucci@tilburguniversity.edu (D. Di Nucci); d.a.tumburri@tue.nl (D. A. Tamburri) GLOBE https://www.gemmacatolino.com/ (G. Catolino); https://dardin88.github.io/ (D. Di Nucci) Orcid 0000-0002-4689-3401 (G. Catolino); 0000-0002-3861-1902 (D. Di Nucci); 0000-0003-1230-8961 (D. A. Tamburri) © 2021 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0). CEUR Workshop Proceedings http://ceur-ws.org ISSN 1613-0073 CEUR Workshop Proceedings (CEUR-WS.org) Organizing Committee • Gemma Catolino, Tilburg University/JADS • Dario Di Nucci, Tilburg University/JADS • Damian A. Tamburri, Eindhoven University of Technology/JADS Program Committee • Anthony Cleve, University of Namur • Eleni Constantinou, Eindhoven University of Technology • Coen De Roover, Vrije Universiteit Brussel • Serge Demeyer, Universiteit Antwerpen • Xavier Devroey, University of Namur • Mohammad Ghafari, University of Bern • Slinger Jansen, Utrecht University • Julia Lawall, Inria/LIP6 • Ivano Malavolta, Vrije Universiteit Amsterdam • Tom Mens, University of Mons • Mike Papadakis, University of Luxembourg • Ayushi Rastogi, University of Groningen • Gregorio Robles, Universidad Rey Juan Carlos • Romain Rouvoy, University of Lille • Alexander Serebrenik, Eindhoven University of Technology • Stefano Zacchiroli, University Paris Diderot and Inria • Andy Zaidman, Delft University of Technology • Vadim Zaytsev, University of Twente