The macroscopic model of solid-solid phase change presented makes use of internal variables to represent the phase fractions and the local strains. As such, it can be cast in the frame-work of standard materials with internal constraints. These constraints are accounted for by Lagrange's multipliers. Reversible or irreversible phase changes are considered in a general way. Material stability is also discussed. Two examples are provided to illustrate the application of the proposed model to brittle damage and to shape memory materials. This model enable to solve boundary value problems as it is shown for the anti-plane shear crack one.