This book constitutes the refereed proceedings of the 23rd Brazilian Symposium on Formal Methods, SBMF 2020, which was supposed to take place in Ouro Preto, Brazil, in November 2020. Instead the symposium took place virtually due to the COVID-19 pandemic.The 10 regular papers presented together with 3 invited talks in this book were carefully reviewed and selected from 17 submissions. The papers are organized in topical sections such as: experience reports; models, languages and semantics; and software product lines.Chapter 'Safety Assurance of a High Voltage Controller for an Industrial Robotic System' is available open access under a Creative Commons Attribution 4.0 International License via link.springer.com.