This open access book constitutes the proceedings of the 23rd International Conference on Foundations of Software Science and Computational Structures, FOSSACS 2020, which took place in Dublin, Ireland, in April 2020, and was held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2020. The 31 regular papers presented in this volume were carefully reviewed and selected from 98 submissions. The papers cover topics such as categorical models and logics
language theory, automata, and games
modal, spatial, and temporal logics
type theory and proof theory
concurrency theory and process calculi
rewriting theory
semantics of programming languages
program analysis, correctness, transformation, and verification
logics of programming
software specification and refinement
models of concurrent, reactive, stochastic, distributed, hybrid, and mobile systems
emerging models of computation
logical aspects of computational complexity
models of software security
and logical foundations of data bases.