Contributed by world-renowned specialists on the occasion of Paul Germain’s 80th birthday, this text reflects the foundational works and the intellectual influence of this author. It presents the realm of modern thermomechanics with its wealth of applications to the behaviour of materials, whether solid or fluid. The 31 contributions follow an autobiographical sketch by Paul Germain, and highlight the power of a methodological approach to the phenomenology of many materials. This approach combines thermodynamics and continuum theory in order to provide exploitable, thermodynamically admissible models of a large variety of behaviours and phenomena, including those of diffusion, thermoelasticity, viscoplasticity, relaxation, hysteresis, wetting, shape-memory effects, growth, phase transitions, stability, fracture, shocks, machining of materials, microstructured solids, and complex fluids. The text should be useful for graduate students, researchers, and engineers in mechanical engineering and materials science.