||This study is concerned with the viscoplastic behaviour of polymers. A modified viscoplastic Bodner–Partom model was extended to include successively the post-yield (strain softening and strain hardening) and the pre-yield behaviour. In order to identify material parameters of the constitutive law, an analytical scheme and a numerical method based on evolutionary algorithms were developed. The capacity of the proposed viscoplastic approach is investigated for a representative glassy polymer (polycarbonate). The results and the efficiency of both approaches are discussed.