Recent research has considered the relationship between Stonehenge and sites in south-west Wales, raising questions about whether the first monument at Stonehenge copied the form of an earlier stone circle at Waun Mawn and how the relationship between these sites was connected with the transport of bluestones between the different regions. But Stonehenge and Waun Mawn are not the only prehistoric sites in Britain and Ireland that share architectural elements and hint at social connections across vast distances of land and sea. This debate article explains how the questions raised about these Late Neolithic monuments can and should be applied to other monumental complexes to explore this insular phenomenon.