Studies of dynamic crack propagation and arrest in polymeric materials are generally interpreted using rate-independent elastic analyses. To ascertain the importance of the viscoelastic constitutive behavior exhibited by polymers that is neglected in these approaches, a simple mathematical model for dynamic viscoelastic crack propagation in wedge-loaded double cantilever beam (DCB) test specimens has been developed. Computational results have been obtained for four different polymers using a three-parameter solid linear viscoelastic constitutive representation. In comparing these results with rate-independent elastic behavior, it is found that significant differences in the crack propagation/arrest process do exist. However, close correlations can nevertheless be obtained if, in displaying experimental results, proper account is taken of the viscoelastic properties.