This thesis examines the development of children's disability concepts from a domain-specific cognition perspective. Previous research into children's concepts of disability is lacking and has been rarely linked to cognitive developmental theories. One particular set of theories suggest that children represent knowledge in domain-specific ways and that prior to formal education, children evidence three foundational knowledge domains; a naive physics, a naive psychology and a naïve biology, which provide causal-explanatory frameworks for interpreting everyday events (Wellman & Gelman, 1992; Hirschfeld & Gelman, 1994). Children's disability concepts are employed to explore how children utilise these foundational knowledge domains in their reasoning of complex phenomena. There were two principal objectives. Firstly, to examine the role of core knowledge domains in children's reasoning about disability and how this may change with age. Secondly, to provide a more comprehensive overview of the content, structure and development of children's disability concepts. Studies la and lb explored which core knowledge domains children use to reason about disability. Using a semi-structured interview schedule, four-five, six-seven, nine-ten and eleven-twelve year-olds' (N = 77) were asked open-ended questions about the consequences (Study la), causes, controllability and chronicity of different disabilities (Study lb). The results showed that by age seven, children's disability concepts are mainly conceptualised within naïve physics and naïve biology. The use of multiple causal-explanatory frameworks did not emerge until eleven years of age. Older children had significantly more cohesive concepts of disability and were able to differentiate the causes of various disabilities. The results showed an early appreciation of the physical and biological nature of disabilities and highlights methodological limitations of open-ended interview methods. Study 2 examined four-five, six-seven and ten-eleven year-olds' (N = 79) causal conceptions of disability more directly and explored the issue of experience in children's disability concepts. Children with and without classroom contact with peers with disabilities were asked to consider the appropriateness of causes of disability relating to each of the foundational knowledge domains (physical, biological and social/psychological), using a forced-choice response scale. The results showed that children of all ages rate biological and physical explanations as significantly more appropriate causes of disability than social/psychological ones. No significant effects of classroom contact were found. The findings highlight the abstract and implicit nature of young children's causal concepts of disability and suggest that these causal concepts were not influenced significantly by direct social contact.