The problem of side-information scalable source coding is considered in this work, where the encoder constructs a progressive description, such that the receiver with high quality side information will be able to truncate the bitstream and reconstruct in the rate distortion sense, while the receiver with low quality side information will have to receive further data in order to decode. We provide inner and outer bounds for general discrete sources. The achievable region is shown to be tight for the case that either of the stages requires a lossless reconstruction. Furthermore we show that the gap between the achievable region and the outer bounds can be bounded by a constant when square error distortion measure is used. Complete characterization is provided for the important quadratic Gaussian source with jointly Gaussian side-informations, where the outer bounds match the achievable region. Partial result is provided for the doubly symmetric binary source with Hamming distortion when the worse side information is a constant, for which one of the outer bound is strictly tighter than the other one.