Complexity issues for the iterated h-preorders -- On the Uniform Distribution of Regular Expressions -- Deterministic one-way simulation of two-way deterministic finite automata over small alphabets -- Sync-Maximal Permutation Groups Equal Primitive Permutation Groups -- Commutative Regular Languages with Product-Form Minimal Automata -- State Complexity Bounds for Upward and Downward Closures on Commutative Languages and Commutative Group and Commutative Aperiodic Languages -- More on the Descriptional Complexity of Compositions of Finite Automata -- Width Measures of Alternating Finite Automata -- Partial Derivative Automaton by Compressing Regular Expressions -- State Complexity of Partial Word Finite Automata -- State complexity of union and intersection on graph-walking automata -- Gray cycles of maximum length related to $k$-character substitutions -- Automata Equipped with Auxiliary Data Structures and Regular Realizability Problems -- Disambiguation of Weighted Tree Automata -- Image-Binary Automata -- Improved constructions for succinct affine automata.

This book constitutes the proceedings of the 23rd International Conference on Descriptional Complexity of Format Systems, DCFS 2021, which was supposed to take place in Seoul South Korea in June 2021, but the conference was canceled due to the COVID-19 crisis. The 16 full papers presented in this volume were carefully reviewed and selected from 21 submissions. The conference focus to all aspects of descriptional complexity-the costs of description of objects in various computational models such as Turing machines, pushdown automata, finite automata or grammars.