Hybrid lipid-polymer nanoparticles have demonstrated potential as drug delivery vehicles. The current proposal aims to use small angle neutron scattering (SANS) in combination with contrast variation to determine the detailed molecular structure of the drug-containing hybrid lipid-polymer nanoparticles, as well as their component lipid vesicles and polymeric nanoparticles. SANS coupled with contrast variation will allow us to establish precisely how much lipid is required to reproducibly and reliably coat the various sized polymeric NPs without using so much lipid so that excess vesicles are present. The information gained from SANS will be important in optimising the hybrid lipid-polymer formulations.