text: Most IPNs do not interpenetrate completely on a molecular scale, but rather form small dispersed or bicontinuous phase morphologies with characteristic length scales on the order of tens of nanometers. However, since these length scales are relatively small, they are often considered homogeneous on a macroscopic scale. The characteristic lengths associated with these domains often scale with the length of chains between crosslinks, and thus the morphology of the phases is often dictated by the crosslinking density of the constituent networks. The kinetics of phase separation in IPNs can arise from both nucleation and growth and spinodal decomposition mechanisms, with the former producing discrete phases akin to dispersed spheres and the latter forming bicontinuous phases akin to interconnected cylinders. Contrary to many typical phase separation processes, coarsening, where the length scale of the phases tends to increase over time, can be impeded by the formation of crosslinks in either network. Furthermore, IPNs are often able to maintain these complex morphologies over long periods of time compared to what could be achieved by simple polymer blends.