Following recent interest in constructing large self-deployable structures made of reinforced polymer materials, this paper presents a detailed study of viscoelastic effects in folding, stowage, and deployment of tape-springs which often act as deployment actuators in space structures. Folding and stowage behavior at different temperatures and rates are studied. It is found that the peak load increases with the folding rate but reduces with temperature. It is also shown that a load reduction of as much as 60% is possible during stowage due to relaxation behavior. Deployment behavior after significant load relaxation demonstrates features distinct from elastic tape-springs. It starts with a short dynamic response, followed by a quasi-static deployment, and ends with a slow creep recovery process. A key feature is that the localized fold stays stationary throughout deployment. Finite element simulations that incorporate an experimentally characterized viscoelastic material model are presented and found to capture the folding and stowage behavior accurately. The general features of deployment response are also predicted, but with larger discrepancy.