- Development of damage in composite laminates is modelled by a set of ordinary differential equations describing the temporal evolution of the internal state variables that characterize damage. The internal state variables are chosen in the form of a set of second order tensors, each element of the set representing the internal state in a given mode of damage. The formulation of the evolution equations follows the general formulation set forth by Coleman and Gurtin in their work on thermodynamics with internal state variables. The form of the evolution equations is restricted by the material symmetry in addition to the thermodynamical restrictions investigated by Coleman and Gurtin. The resulting equations are sought verified by limited experimental data and good correlations are obtained.