The paper reviews the kinetics and morphology of the various phase-segregation processes that may be encountered in multiphase polymer flow systems. A primary aim of this review has been to investigate how certain processing variables influence the polymer structure and the degree of phase segregation in various geometries of interest. A pronounced distinction is made between the terms “diffusion” and “field-induced segregation.” The former is conventionally regarded as the mass transfer resulting from Brownian motion and, in any case, is a randomizing process. The latter, on the other hand, implies “flow” of matter subject to a “driving potential.” As opposed to diffusion in the classical sense, field-driven transport may be affectedagainstthe concentration gradient. It is seen that the application of an appropriate lateral field generates transversal migration of suspended material or additive and, in certain cases, the segment domains in the “matrix” polymer. In particular, the potential of shear fields to generate locally segregated flow structures, which might be preserved during the fabrication procedure, has been assessed. It has been shown that with an expression for the lateral “drift” velocity, the time and space evolution of the cross-flow concentration profile may be obtained from the continuity relation. Even though one finds a surprisingly large variety of driving forces available for segregation transport, the efficacy of highly specific processes lies in the novel application of boundary conditions. Convection promoted shear transport has been cited as a relevant example with an initial condition which specifies a cross-flow velocity component in an existing shear field. Other promising configurations include the sequential flow in two-phase flow and rheological segregation. The investigation reveals that migratory transport in polymer processing channels has the potential to generate localized changes in the polymer morphology and structure, apart from affecting phase redistribution of additive species (both solid and liquid systems) on a more global scale. Experimental evidence obtained on the phase fractionation in polydispersed low-density polyethylene (LDPE) and thermosetting polyurethane (PU) clearly demonstrates the phenomenon.