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: 1. 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. 2. The damping-solvent extraction method permits the analysis of a bounded medium only. 3. The doubly-asymptotic