This book constitutes the proceedings of the 40th International Conference on Application and Theory of Petri Nets and Concurrency, PETRI NETS 2019, held in Aachen, Germany, , in June 2018. Petri Nets 2019 is co-located with the 19th International Conference on Application of Concurrency to System Design, ACSD 2019. The 23 regular and 3 invited papers presented together in this volume were carefully reviewed and selected from 41 submissions. The focus of the conference is on following topics: Models, Tools, Synthesis, Semantics, Concurrent Processes, Algorithmic Aspects, Parametrics and Combinatorics, and Models with Extensions.