Multi-scale ordering of materials is central for the application of molecular systems(1-3) in macroscopic devices(4,5). Self-assembly based on selective control of non-covalent interactions(6-8) provides a powerful tool for the creation of structured systems at a molecular level, and application of this methodology to macromolecular systems provides a means for extending such structures to macroscopic length scale(9-11). Monolayer-functionalized nanoparticles can be made with a wide variety of metallic and nonmetallic cores, providing a versatile building block for such approaches. Here we present a polymer-mediated ＇bricks and mortar＇ strategy for the ordering of nanoparticles into structured assemblies. This methodology allows monolayer-protected gold particles to self-assemble into structured aggregates while thermally controlling their size and morphology. Using 2-nm gold particles as building blocks, we show that spherical aggregates of size 97 +/- 17 nm can be produced at 23 degrees C, and that 0.5-1 mu m spherical assemblies with (5-40) x 10(5) individual subunits form at -20 degrees C. Intriguingly, extended networks of similar to 50-nm subunits are formed at 10 degrees C, illustrating the potential of our approach for the formation of diverse structural motifs such as wires and rods. These findings demonstrate that the assembly process provides control over the resulting aggregates, while the modularity of the ＇bricks and mortar＇ approach allows combinatorial control over the constituents, providing a versatile route to new materials systems.