This paper is concerned with the thermal degradation of poly(vinyl alcohol), both in the solid and molten state. Initially, thermal degradation in the solid state was considered to be due to the elimination of hydroxyl side groups, but this process should have produced appreciable amounts of isolated and conjugated polyenes in the degradation residue and small amounts of carbonyl group were detected. Side group elimination was followed by a reduction in the melting point and the degree of crystallinity. In the molten state, thermal degradation led to the production of volatile saturated and unsaturated aldehydes and ketones, as well as water. It was considered that the greater flexibility of the polymer chains in the melt facilitated fragmentation of the chain and elimination of chain segments.