The properties of polymer/semiconducting nanoparticle (NP) composites-materials used in hybrid, bulk-heterojunction photovoltaic materials-are dependent on the interaction of the NPs and polymer. Composite films of water soluble polymers and CdS NPs have been produced both by synthesizing the NPs within the polymer matrix and by adding the CdS NPs, containing a capping agent, to the polymer. The composites have been characterized by microscopy as well as 1H, 13C and 113Cd solid-state NMR. When synthesizing the NPs within the polymer, the polymer matrix plays a role in the cadmium sulfide NP nucleation, growth and structure. In the blended system, the dominant interaction between the glycerol capping agent and sulfonated polymer is observed to be hydrogen bonding.