The goal of this conference series is to bring together researchers working on mathematical foundations of quantum physics, quantum computing, spatio-temporal causal structures, and related areas such as computational linguistics. Of particular interest are topics that use logical tools, ordered algebraic and category-theoretic structures, formal languages, semantical methods and other computer science methods for the study of physical behaviour in general. Over the years, the QPL conference series has evolved from an initial focus on Quantum Programming Languages, to a more broad set of topics in the intersection of Quantum Physics and Logic. The aim is to nourish interaction between modern computer science logic, quantum computation and information, models of causality, and quantum foundations. 21st International Conference on Quantum Physics and Logic (QPL 2024). Buenos Aires, July 15–19, 2024. 20th International Conference on Quantum Physics and Logic (QPL 2023). Paris, July 17–21, 2023. 19th International Conference on Quantum Physics and Logic (QPL 2022). Oxford, June 27–July 1, 2022. 18th International Conference on Quantum Physics and Logic (QPL 2021). Gdansk, Poland, June 7–11, 2021. 17th International Conference on Quantum Physics and Logic (QPL 2020). Paris, June 2–6, 2020. 16th International Conference on Quantum Physics and Logic (QPL 2019). Orange, California, June 10–14, 2019. 15th International Conference on Quantum Physics and Logic (QPL 2018). Halifax, Canada June 3–7, 2018. 14th International Conference on Quantum Physics and Logic (QPL 2017). Nijmegen, July 3–7, 2017. 13th International Conference on Quantum Physics and Logic (QPL 2016). Glasgow, June 6–10, 2016. 12th International Workshop on Quantum Physics and Logic (QPL 2015). Oxford, July 15–17, 2015. 11th International Workshop on Quantum Physics and Logic (QPL 2014). Kyoto, June 4–6, 2014. 10th International Workshop on Quantum Physics and Logic (QPL 2013). Barcelona, July 17–19, 2013. 9th International Workshop on Quantum Physics and Logic (QPL 2012). Brussels, October 10–12, 2012. 8th International Workshop on Quantum Physics and Logic (QPL 2011). Nijmegen, October 27–29, 2011. 7th International Workshop on Quantum Physics and Logic (QPL 2010). Oxford, May 29-30, 2010. 6th International Workshop on Quantum Physics and Logic (QPL 2009). Oxford, April 8-9, 2009. 5th International Workshop on Quantum Physics and Logic (QPL 2008). Reykjavik, July 12-13, 2008. 4th International Workshop on Quantum Programming Languages (QPL 2006). Oxford, July 17-19, 2006. 3rd International Workshop on Quantum Programming Languages (QPL 2005). Chicago, June 30 - July 1, 2005 (affiliated Workshop of LICS 2005). 2nd International Workshop on Quantum Programming Languages (QPL 2004). Turku, Finland, July 12-13, 2004 (affiliated Workshop of LICS 2004). 1st International Workshop on Quantum Programming Languages (QPL 2003). Ottawa, Canada, June 15-16, 2003 (affiliated Workshop of Fields 2003). Peter Selinger / Department of Mathematics and Statistics / Dalhousie University selinger@mathstat.dal.ca / PGP key