The self-assembly of block copolymers in emulsion droplets is a promising strategy to prepare polymer particles with a well-defined and tuneable nanostructure. Block copolymers exhibit rapid assembly kinetics, macroscopic ordering into self-assembled morphologies, tolerance to high loading of functional additives, and the possibility to manipulate the domain spacing by tuning the polymer chain length and structure. Constraining the self-assembly of block copolymers introduces structural frustration, entropy losses, surface-polymer interactions, and structural and symmetry breaking which can be exploited to control the self-assembly process.  All these aspects direct the assembly of the macromolecular chains, enabling the formation of a rich variety of complex structures – often thermodynamically unstable – that are challenging to obtain when processing BCPs into films from a polymer melt or solution.