Direct simulations of solidification processes that account for all space and time scales are often beyond the reach of current computational power, To overcome this limitation micro-macro approaches that incorporate the effects of small-scale phenomena into large-scale process models have been developed. An important small-scale solidification phenomenon is microsegregation-the redistribution of rejected solute components at the scale of the solid crystal morphology. This paper outlines a general microsegregation model that not only accounts for many of the critical small-scale phenomena in alloy solidification but also well suited as the micro component of a micro-macro model of metal casting. In the development of this microsegregation model, particular emphasis and testing is placed on alternative treatments of modeling the microscale solute diffusion in the solid phase-the so-called "back-diffusion."