Block copolymer/nanoparticle (BCP/NP) composites have attracted much attention due to their easiness of fabricating nanoscopic hierarchical structures, and significantly enhanced chemical and physical properties of the nanocomposites. Most of the focus in co-assembly of BCPs and NPs has been placed on the controlled alignment of NPs, "passively," in the BCP domain. However, NPs with carefully designed interfacial properties "actively" direct self-assembled structure of BCP in a nonconventional route. Herein, we review recent investigations of the self-assembly of BCP domains in thin films via the addition of structure-directing organic and inorganic NPs. Understanding the phase behavior of BCP/NP coassembly along with the theoretical description can shed a light on the far-reaching potentials to creating nonconventional nanostructures rarely obtained via traditional fabrication tools. (C) 2015 Wiley Periodicals, Inc.