A new process for nanoparticle self-assembly resembles step-growth polymerization and gives scientists a long-desired strategy for predicting nanostructure properties, such as their architecture and size distribution (Science 2010, 329, 197). Self-assembly is a highly attractive phenomenon because it allows scientists to create structures with numerous potential optical, electronic, and magnetic properties for applications ranging from optoelectronics to sensing. Eugenia Kumacheva of the University of Toronto; Michael Rubinstein of the University of North Carolina, Chapel Hill; and colleagues prepared gold nanorods that have arrowhead-shaped ends. They coated the rod shafts with cetyl trimethyl ammonium bromide bilayers and coated the arrowheads with thiol-terminated polystyrene. The rods self-assemble at the arrowhead ends into “nanopolymers,” with the length and branching of the chains controlled by reaction time and conditions much in the same way molecular polymerization reactions are controlled.