Dynamic unbounded medium-structure interactions occur in many fields of engineering and physical science, such as wave propagation in soil-structure and fluid-structure interactions, acoustics and electromagnetism and as diffusion in heat conduction and consolidation. This book presents three novel concepts, based on the finite-element methodology, to model the unbounded medium: * The consistent infinitesimal finite-element cell method, a boundary finite-element procedure, requires the discretization of the structure-medium interface only and is exact in the finite-element sense. It is applied to unbounded media governed by the hyperbolic, parabolic and elliptic differential equations.* The damping-solvent extraction method permits the analysis of a bounded medium only.* The doubly-asymptotic multi-directional transmitting boundary is exact for the low- and high-frequency limits at preselected wave propagation directions. All concepts are explained using simple examples that the reader can follow step by step. A computer program of the consistent infinitesimal finite-element cell method available on disk analyses two- and three-dimensional unbounded and bounded media for the scalar and vector wave equations and the diffusion equation in the frequency and time domains.