Preface

The Sixth International Conference on Applied Category Theory took place at the University of Maryland on 31 July - 4 August 2023, following the previous meetings at Leiden (2018), Oxford (2019), MIT (2020, fully online), Cambridge (2021) and Strathclyde (2022). It was preceded by the Adjoint School 2023 (24 - 28 July), a collaborative research event in which junior researchers worked under the mentorship of experts. The conference comprised 59 contributed talks, a poster session, an industry showcase session, four tutorial sessions and a session where junior researchers who had attended the Adjoint School presented the results of their research at the school. Information regarding the conference may be found at https://act2023.github.io/. ACT 2023 was a hybrid event, with physical attendees present in Maryland and other participants taking part online. All talks were streamed to Zoom and with synchronous discussion on Zulip. Submission to ACT2023 had three tracks: extended abstracts, software demonstrations, and proceedings. The extended abstract and software demonstration submissions had a page limit of 2 pages, and the proceedings track had a page limit of 12 pages. Only papers submitted to the proceedings track were considered for publication in this volume. In total, there were 81 submissions, of which 59 were accepted for presentation and 18 for publication in this volume. Publication of accepted submissions in the proceedings was determined by personal choice of the authors and not based on quality. Each submission received a review from three different members of the programming committee, and papers were selected based on discussion and consensus by these reviewers. The contributions to ACT2023 ranged from pure to applied and included contributions in a wide range of disciplines in science and engineering. ACT2023 included talks in linguistics, functional programming, classical mechanics, quantum physics, probability theory, electrical engineering, epidemiology, thermodynamics, engineering, and logic. Many of the submissions had software demonstrating their work or represented work done in collaboration with industry or a scientific organization. The industry session included 9 invited talks by practitioners using category theory in private enterprise. ACT2023 included four tutorials: David Jaz Myers on Lenses, Paolo Perrone on Markov categories, Dorette Pronk on Double categories, and Evan Patterson and Owen Lynch on AlgebraicJulia. We are grateful to Angeline Aguinaldo, James Fairbanks, Joe Moeller, and Priyaa Varshinee Srinivasan who played various roles in the ACT organization. ACT2023 was sponsored by AARMS (Atlantic Association for Research in the Mathematical Sciences), Conexus, DeepMind, NIST (National Institute of Standards and Technology), PIMS (Pacific Institute for the Mathematical Sciences), Quantinuum, University of Florida and 20 Squares. Sam Staton and Christina Vasilakopoulou Chairs of the ACT 2023 Programme Committee