This review article scrutinizes and reanalyzes the extensively available literature data on the tracer and self chain diffusion coefficients D-tr and D-s along with the corresponding zero-shear viscosity eta(0) to show that D-s proportional to M-v starts with v > 2.0 and converges to the asymptotic scaling exhibited by D-tr proportional to M-2.0 as the molecular weight M increases beyond M/M-e = 10-20, in contrast to the onset of the asymptotic scaling M-3 for eta(0) taking place typically for M/M-e much greater than 10-20. A coherent analysis of these observations leads to the suggestion that the observed crossover in D-s is due to the constraint release effect, which diminishes around M/M-e = 10-20 and is negligible in measurements of D-tr when the matrix molecular weight P is much greater than M. The contour length fluctuation (CLF) effect, which is believed to cause the molecular weight scaling of eta(0) to deviate significantly from its limiting behavior of M-3, has little direct influence on the chain diffusion. The absence of the CLF effect on D-s leads to a much stronger than linear dependence of the product eta(0)D(s) on M, which has been observed previously. (C) 2003 Wiley Periodicals, Inc.