Colloidal microcapsules (MCs) are highly modular, inherently multiscale constructs of capsules stabilized by nano-/microparticle shells, with applications in many areas of materials and biological sciences, such as drug delivery, encapsulation, and microreactors. Until recently, fabrication of colloidal MCs focused on the use of submicron-sized particles because the smaller nanoparticles (NPs) are inherently unstable at the interface owing to thermal disorder. However, stable microcapsules can now be obtained by tuning the interactions between the nanometer-sized building blocks at the liquid-liquid interface. This Review highlights recent developments in the fabrication of colloidal MCs using NPs.