In polymer blends and block copolymers, one constituent (or segment type) is often enriched at the surface. This enrichment has important consequences for a variety of surface functions, including wettability, adhesive interactions, and fouling resistance, and can also influence the structure that forms deeper into the bulk. Herein, we review the thermodynamic principles that control the attraction of polymers toward surfaces, emphasizing cases where entropic effects associated with molecular weight or architecture can compete with enthalpic preferences. While models and simulations have guided our understanding of this interplay, we show that it remains difficult to anticipate the outcomes when using chemically complex materials or nonequilibrium processing conditions. Nevertheless, it is possible to leverage established principles to tailor the wetting of polymers at surfaces, which is important for the design of membranes, coatings, lithographic materials, and thin film electronics.