Unconventional computation and natural computation : 20th International Conference UCNC 2023 Jacksonville FL USA March 13 17 2023 proceedings This book constitutes the proceedings of the 20th International Conference on Unconventional Computation and Natural Computation UCNC 2023 held in Jacksonville FL USA in March 13 17 2023. The UCNC conference series covers fundamental research on computation beyond the standard Turing model including computational models and methods inspired by nature and the computational properties of natural processes