This review briefly describes recent advances on the synthesis of metal hydroxide nanomaterials and their assembly into 3D architectures toward applications of catalysis, adsorption, and energy conversion. The discussion is mainly dedicated to the synthesis strategies toward nanohydroxide-based functional materials. A special attention is focused on two reaction schemes for the preparations of: (1) macroporous (hydr)oxides monoliths and (2) monodispersed hydroxide nanoclusters and mesoporous hydroxides.