We report on the development and validation of a neighbourhood measure of social fragmentation. Firstly, we developed a theoretical model of neighbourhood-level social fragmentation, as the structural antecedent to collective social functioning, with three domains (attachment, resources, and means of sharing of norms and values). Secondly, utilising the New Zealand 1996 and 2001 Censuses, variables were constructed to create the New Zealand Index of Neighbourhood Social Fragmentation (NeighFrag) at the small-area level. Nine census variables contributed sub- stantively to a principal components analysis: homeownership, mobility, marital status, nonfamily households, single-person households, children, immigrants, non-English/Maori speakers, and long- term residents. Thirdly, relationships between NeighFrag and other contextual measures were examined, as well as its relationship with individual perceptions of neighbourhood cohesion. The NeighFrag index had a moderate association with deprivation and social capital. It was inversely associated with individual perception of neighbourhood cohesion in multilevel analyses, after adjust- ing for individual factors and neighbourhood deprivation. Combined, this suggests that NeighFrag provides a meaningful national-level index of neighbourhood social environments for use in analyses. <br><br><b>Keywords:</b> social fragmentation, neighbourhood, social capital, social cohesion, principal components analysis, deprivation
