The overall purpose of this dissertation was to examine the environmental influences on physical activity behaviours among London Ontario children and youth. Three studies were conducted to accomplish this purpose. First, the physical activity levels, within the context of environmental opportunity structures, were quantitatively investigated for youth aged 11-13 years (n=811). The primary purpose of Study 2 was to gain an understanding of grade 7 and 8 students' awareness of neighbourhood environmental influences on their physical activity choices (n=60). To provide a more complete picture of the neighbourhood environment, the secondary purpose was to gain youths' insight into the environmental influences on their food intake. Because parks are known to promote physical activity among children, the purpose of Study 3 was to assess the parents' preferences regarding features of city parks, using London, Ontario as a case study (n=82).