The focus of this paper is on the viscoelastic properties of concentrated polymer solutions and polymer melts. Dynamic mechanical measurements were performed on various polystyrene/ethylbenzene solutions with polymer concentrations ranging from 40% up to 100% and temperatures from T-g + 30 degrees C up to 70 degrees C (230 degrees C for polymer melts). The basis polymers are two commerical grade polystyrenes (BASF) with M(w) = 247 kg/mol and 374 kg/mol, respectively. To avoid solvent loss due to evaporating during the measurements, a special sealing technique was used. A phenomenological model which describes quantitatively the relaxation spectrum of concentrated polymer solutions from the flow regime up to the glass transition regime is developed. The relaxation data of the respective polymer melt and the glass transition temperature of the solution are the only input parameters needed. The temperature dependence is described by a universal, concentration invariant WLF-equation. The relaxation spectra are divided into two parts accounting for the entanglement and the segmental relaxation modes, respectively. The relaxation strength related to the flow and entanglement regime scale with c(2.3), whereas the segmental relaxation strength does not alter with concentration. All relaxation times change with concentration proportional to c(3.5). Flow curves can be calculated from these relaxation spectra and thus, our results are useful for engineering applications.