The area of“polymer blends”has interested many scientists since the 1960s．This is because the polymer blends provide many special and desirable properties．The thermodynamics of the phase behavior and the kinetics of phase separation／dissolution processes play an important part in these applications．In recent years

lots of advancement have been made in both theories and experiments．The statics part of the phase behavior studies are mostly started from the Flory—Huggins mean—field theory．and the kinetics ofphase separation are mostly based on the Cahn-Hilliard-Cook(CHC)linear theory．Many new developments and improvements on theories and new verifications and extensions by experiments have been achieved

including some theoretical and experimental developments in nonlinear phase separation behavior．In this paper

the authors review the scientific development in both the static and kinetic aspects of the spinodal decomposition(SD)．Then

we describe the static scattering experiment

which measures the concentration fluctuations of a binary mixture．After that we present some recent theoretical calculations on the SD of binary polymer system．First

the derivation of CHC theory from generalized Langevin equation is reviewed to provide a microscopic pietore for the phenomenological mean-field theory of CHC．Then a mold—coupling calculation Was used to extend the SD theory into the nonlinear region．The quantitative nature of the calculation is demonstrated by a comparison with the dissolution study of a polymer blend subjected to SD for a short period．Finally

some recent studies on shear dependence of the phase behavior and possible future potentials and directions in this field have also been discussed.