Disclosed are nanoparticles comprising a block copolymer and optionally one or more active agent(s), compositions comprising said nanoparticles and methods of preparing said nanoparticles. The block copolymer comprises blocks (i) a first polymer that is a polyester or polyamide and (ii) a second polymer comprising a hydrocarbon chain containing ester or ether bonds with hydroxyl number ≧10. The active agent(s) may be present within the nanoparticles or on the surfaces of the nanoparticles. The nanoparticles may optionally be associated with a surface-modifying moiety such that they are useful as drug delivery and molecular imaging devices. The surface-modifying moiety may target the nanoparticles to a desired target, cell, tissue or biomarker.
