Abstract Polymer nanocapsules ( PNCs ) are an important class of nanocarriers, but applications of conventional non‐crosslinked PNCs have been significantly limited because they are susceptible to environmental conditions. Synthesis and applications of crosslinked PNCs ( CPNCs ) with robust covalently stabilized nanostructures have attracted great interest over the past decade. Three major categories of template synthesis approaches for the preparation of CPNCs have been established: (1) cavitation of shell‐crosslinked nanostructures, (2) vesicle‐based crosslinking and (3) emulsion interfacial crosslinking. This article provides a critical and comprehensive review of these approaches. Several special cases of the synthesis of CPNCs are also reviewed. © 2016 Society of Chemical Industry