A description of a low-dimensional deterministic chaotic system in terms of unstable periodic orbits (cycles) is a powerful tool for theoretical and experimental analysis of both classical and quantum deterministic chaos, comparable to the familiar perturbation expansions for nearly integrable systems. The infinity of orbits characteristic of a chaotic dynamical system can be resummed and brought to a Selberg product form, dominated by the short cycles, and the eigenvalue spectrum of operators associated with the dynamical flow can then be evaluated in terms of unstable periodic orbits. Methods for implementing this computation for finite subshift dynamics are introduced.