Nanoparticle (NP)-assembled microcapsules represent a new class of hollow-sphere material, in which materials properties can be ‘programmed’ by way of NP and polymer compositions. Synthesis is based on a sequential self-assembly of NPs and polymer macromolecules. Reported by Wong and co-workers on p. 1145, this rapid, green synthesis technique applies to a wide spectrum of colloidal species and permits non-destructive encapsulation of water-soluble compounds. The inside cover shows a confocal microscopy image of water-filled microcapsules composed of silica NPs and a fluorescence-labelled polymer. The scale bar is 20 μm. The inset shows a simplified illustration of the microcapsule assembly process.