The properties of the alpha- and Johari-Goldstein beta -relaxations in conjunction with configurational entropy data are used to show how cooperativity of the dynamics of poly(vinylacetate) develops as temperature is decreased towards T-g from above. Such behavior is also characteristic of small molecule glass-forming liquids, demonstrating that the combined effects of configurational entropy changes and intermolecular coupling underlie structural relaxation phenomena. Any theoretical model must include both thermodynamics and many-body dynamics in order to accurately describe the general properties of the glass transition.