Amorphous polymers are composed of entangled (spaghetti-like) long chain hydrocarbon molecules. Under load, these deform instantaneously in an elastic manner but, thereafter, begin to slide over one another - resulting in creep and stress relaxation. These materials therefore exhibit both solid- and fluid-like behaviour. The mathematical response-modelling of these materials usually begins by either augmenting the classical elasticity equations with a Volterra (memory) integral; or by adjoining to them a set of evolution equations for internal state variables which capture the internal dynamics. Both approaches will be described, along with space-time finite element approximations and recently-derived a posteriori error estimates.