This volume contains the proceedings of the 23rd International Conference on Quantum Physics and Logic (QPL 2026), which was held from August 17 to August 21 2026, in Amsterdam, The Netherlands, organized by the University of Amsterdam. QPL is an annual conference that brings together academic and industry researchers working on topics ranging from basic research in the foundations of physics to applications in quantum computing and communication, both for near-term quantum hardware and future large-scale, fault-tolerant devices. The conference places particular emphasis on the application of formal algebraic, logical, compositional, and categorical structures to quantum theory and related areas. Work applying quantum-inspired techniques and structures to other fields such as (classical) computation, linguistics, artificial intelligence, and causality is also welcome.

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