Bonding Grammars -- Card Based Overwriting Protocol for Equality Function and Applications -- A methodology for comparing and benchmarking quantum devices -- Benchmarking the D Wave quantum annealer as a Sparse Boltzmann Machine recognition and timing performances -- Software Testing in Computable Analysis -- Card Based Cryptography Meets 3D Printer -- Self Assembly of Patterns in the abstract Tile Assembly Model -- Rate independent continuous inhibitory chemical reaction networks are Turing universal -- Entropy Transformation Measures for Computational Capacity -- Quantum Property Testing Algorithm for the Concatenation of Two Palindromes Language -- On the Simulation Power of Surface Chemical Reaction Networks -- A Representative Framework for Implementing Quantum Finite Automata on Real Devices -- A general design method for scaffold free DNA wireframe nanostructures -- Automated rendering of multi stranded DNA complexes with pseudoknots -- A Novel Oscillator Ising Machine Coupling Scheme for High Quality Optimization -- Agent Motion Planning as Block Asynchronous Cellular Automata Pushing Pulling Suplexing and More -- Minimizing Cycles in Reaction Systems -- Computing Threshold Circuits with Bimolecular Void Reactions in Step Chemical Reaction Networks -- High Quality Circuit based 3-SAT Mappings for Oscillator Ising Machines.

This book constitutes the proceedings of the 21st International Conference on Unconventional Computation and Natural Computation, UCNC 2024, held in Pohang, South Korea, during June 17-21, 2024. The 19 full papers included in this book were carefully reviewed and selected from 27 submissions. Typical, but not exclusive, UCNC topics of interest include amorphous computing, cellular automata, chaos and dynamical systems-based computing, cellular, chemical, evolutionary, bacterial, molecular, neural and optical computing, collision-based computing, quantum computing, DNA computing, membrane computing, material computing and programmable matter, super-Turing computation, swarm intelligence, and other nature-inspired algorithms.