There is still plenty of room in the middle between 1 nm and 100 nm, an interesting length scale commensurate with natural physical phenomena (e.g., exciton Bohr radii, superparamagnetic limit, visible to IR localized surface plasmon resonances) and the typical size range of colloidal nanocrystals (NCs). Colloidal nanocrystals (NCs) can be exquisitely tailored in size, shape, and composition and thus, in their optical, electronic, magnetic, thermal, chemical, and mechanical properties. As colloids, they can be self- or directed to self-assemble using solution-based coating, printing, and imprinting techniques into 2D and 3D materials hierarchically structured from the nano to micro scales. In this talk, I will describe our work using NCs as artificial atoms to build materials and devices with extraordinary structures and functions. We design materials and devices from single- and multiple-types of NCs and exploit what makes NCs different from bulk materials, notably their size and composition dependent physical properties and the ability to chemically and thermally address NCs to exchange, strip, or add surface atoms, ions, and molecules during or post-deposition. By designing NC materials with multiple functions, we demonstrate flexible NC electronics and the first NC integrated circuits, large-area 2D and 3D optical metamaterials that operate as reconfigurable chiral photonic and chiral luminescent devices and optical sensors, and magnetically- and acoustically-driven active matter.