Star polymers are comprised of multiple arms or branches radiating from a central point or core and have been of huge scientific interest since they were first prepared sixty years ago, as a result of their unique physical properties. Star polymers are not just an academic curiosity, but are currently employed or under investigation in a wide range of industries and commercial materials ranging from engine oils and coating technologies to contact lenses and biomedical devices. Although there are many different types of star polymers and methods for their synthesis, recent advances in the field of controlled radical polymerisation have enabled the facile production of complex star polymer architectures from a large range of monomer families, without the requirement of highly stringent reaction conditions. In particular, well-defined, nanometre scale core cross-linked star (CCS) polymers, which are readily accessible by controlled radical polymerisation techniques, have been increasingly prominent in the scientific literature. As a result, this feature article provides a comprehensive review covering the development, functionalisation, physical properties and application of core cross-linked star polymers prepared by controlled radical polymerisation and the arm-first approach