Shear banding occurs in the flow of complex fluids: various types of shear
thinning and shear thickening micelle solutions and liquid crystals. In ord
er to cope with the strongly inhomogeneous interface between the bands, con
stitutive models used in standard rheology must be supplemented by non-loca
l terms. This leads rather generally to non-linear partial differential equ
ations of the reaction-diffusion type. We use this formalism in order to ex
plain some observed experimental features and as a guide for future researc
h in this field.