Childhood overweight and obesity have been at the forefront of the public health agenda for a decade. Within this time a paradigm shift within medical and social sciences has altered the focus on personal determinants of obesity towards environmental and societal level influences. The neighbourhood environment is implicated in health, encompassing all aspects of the energy balance equation (i.e. physical activity (PA), diet and weight). Relatively little is known about neighbourhood-level health associations in young people, particularly within the UK. At the heart of this thesis is the Children’s Neighbourhood Environment Study (CNES) which aimed to identify physical environment correlates and mediating factors of PA and dietary intake behaviours and resultant weight outcomes in young people (10–11 years) within the North East of England. In response to persistent recommendations in obesogenic environment literature CNES applied a cross-disciplinary mixed-methods approach to research. This comprised: focus groups, participant-reported PA and dietary behaviours, participant and parent reported neighbourhood enviorment perceptions, objective (utilizing a GIS-based approach) and subjective neighbourhood environment measurement and appraisal. Youth PA showed statistically significant positive association with park and green space access, total street length and total road length but inverse association with mixed land use; associations with other neighbourhood features did not reach statistical significance. Dietary intake showed no statistically significant association with the neighbourhood environment. Elevated weight status showed statistically significant positive association with mixed land use and the absence of cycling facilities; associations with other neighbourhood features did not reach statistical significance. Page ii of 416 CNES adopted a robust and comprehensive cross-disciplinary approach, the first study of its kind in the UK. It implicates the neighbourhood environment in enabling and disabling PA behaviours and weight outcomes in young people. CNES has successfully identified strategic areas to target public health intervention and inform urban planning to facilitate health.