Constitutes the refereed proceedings of the 5th International Conference on Unconventional Computation, UC 2006, held in York, UK, in September 2006. This title presents 17 revised full papers together with four invited full papers.

Invited Papers.- Graph Machines and Their Applications to Computer-Aided Drug Design: A New Approach to Learning from Structured Data.- Rational Models of Cognitive Control.- Fault-Tolerance in Biochemical Systems.- Optical Computing and Computational Complexity.- Regular Papers.- If a Tree Casts a Shadow Is It Telling the Time?.- Peptide Computing – Universality and Theoretical Model.- Handling Markov Chains with Membrane Computing.- Approximation Classes for Real Number Optimization Problems.- Physical Systems as Constructive Logics.- On Spiking Neural P Systems and Partially Blind Counter Machines.- Chemical Information Processing Devices Constructed Using a Nonlinear Medium with Controlled Excitability.- Flexible Versus Rigid Tile Assembly.- On Pure Catalytic P Systems.- Mapping Non-conventional Extensions of Genetic Programming.- The Number of Orbits of Periodic Box-Ball Systems.- The Euclid Abstract Machine: Trisection of the Angle and the Halting Problem.- 1/f Noise in Elementary Cellular Automaton Rule 110.- A Light-Based Device for Solving the Hamiltonian Path Problem.- Optimizing Potential Information Transfer with Self-referential Memory.- On the Power of Bio-Turing Machines.- Ergodic Dynamics for Large-Scale Distributed Robot Systems.