This book constitutes the proceedings of the 20th International Colloquium on Theoretical Aspects of Computing, ICTAC 2023, which took place in Lima, Peru, during December 4–8, 2023.The 20 full papers presented in this volume together with 3 invited papers and 1 tool paper were carefully reviewed and selected from 40 submissions.

Optimal Route Synthesis in Space DTN using Markov Decision Processes.- Modelling and Verifying Robotic Software that use Neural Networks.- A game-theoretic approach to indistinguishability of winning objectives as user privacy.- Learning Attack Trees by Genetic Algorithms.- The Landscape of Computing Symmetric $n$-Variable Functions with $2n$ Cards.- On the complexity of reasoning in Kleene algebras with commutativity conditions.- Towards the Complexity Analysis of Programming Language Proof Methods.- A Dynamic Temporal Logic for Quality of Service in Choreographic Models.- Interactive Matching Logic Proofs in Coq.- An Autonomous Data Language.- Formal Language Semantics for Triggered Enable Statecharts with a Run-to-Completion Scheduling.- Strong Call-by-Value and Multi Types.- Algorithms for Checking Intersection Non-emptiness of Regular Expressions.- Realisability of Global Models of Interaction.- Efficient Reactive Synthesis Using Mode Decomposition.- A Categorical Approach to Synthetic Chemistry.- Closure and Decision Properties for Higher-Dimensional Automata.- Robustness in Metric Spaces over Continuous Quantales and the Hausdorff-Smyth Monad.- Moggi Synchronous Agents, Verification, and Blame – A Deontic View.- Store Locally, Prove Globally.- Denotational Semantics for Symbolic Execution.- TOOL PAPER: Tessla-ROS-Bridge - Runtime Verification of Robotic Systems.- Simplifying process parameters by unfolding algebraic data types.- Modular Soundness Checking of Feature Model Evolution Plans.