This subject provides an introduction to the mechanical behavior of materials, from both the continuum and atomistic points of view. At the continuum level, we learn how forces and displacements translate into stress and strain distributions within the material. At the atomistic level, we learn the mechanisms that control the mechanical properties of materials. We will consider: linear elasticity (recoverable deformation at small displacements), viscoelasticity (behavior intermediate to that of an elastic solid and that of a viscous fluid), plasticity (permanent deformation), creep in crystalline materials (time dependent behavior), brittle fracture (rapid crack propagation) and fatigue (failure due to repeated loading of a material). Examples are drawn from metals, ceramics, glasses, polymers, biomaterials, composites and cellular materials.