Two aspects of the mechanical behaviour of solid polymers are reviewed: (i) anisotropic mechanical behaviour of oriented polymers, and (ii) nonlinear viscoelastic behaviour. In the case of anisotropic behaviour, the discussion includes a comprehensive account of progress to date in obtaining experimental data, together with recent attempts at understanding the behaviour in structural terms. The discussion of nonlinear viscoelastic behaviour, on the other hand, is almost entirely at a phenomenological level. Here it is attempted to bring together the many different approaches and to show their common relationships, particularly between the engineering formulations and those based on continuum mechanics.