Gold nanoparticles (<or=1 nm) have been encapsulated inside cucurbit[7]uril (CB[7]) by vapor deposition or chemical reduction in aqueous solutions. CB[7] has unique host properties compared with CB[5] and CB[6]. The particle size distribution obtained with CB[5] and CB[6] is similar to that obtained in the absence of CBs and the particles obtained are much too large to be incorporated inside the organic capsules. When gold nanoparticles are prepared inside CB[7] the resulting supramolecular assembly has shape-selective properties for gold interactions with amines, cyanide, and quaternary ammonium ions. Thus, CB[7] has the potential to be used in applications such as selective adsorption, sensing, and catalysis.