We consider type IIB string in the two plane-wave backgrounds which may be interpreted as special limits of the AdS3 × S supported by the NS-NS or R-R 3-form backgrounds. The NS-NS plane-wave string model is equivalent to a direct generalization of the NappiWitten model, with its spectrum being similar to that of strings in constant magnetic field. The R-R model can be solved in the light-cone ...