The paper describes and evaluates the theoretical underpinnings of the International Classification of Functioning, Disability and Health (ICF), and develops the proposition that its conceptual framework provides a coherent, if uneven, guide through the competing conceptions of disability. To date, however, there has been little evaluation of the theoretical efficacy of the ICF. In seeking to redress this, the paper develops the argument that the ICF fails to specify, in any detail, the content of some of its main claims about the nature of impairment and disability. This has the potential to limit its capacity to educate and influence users about the relational nature of disability. The paper develops the contention that three parts of the ICF require further conceptual clarification and development: (a) (re)defining the nature of impairment; (b) specifying the content of biopsychosocial theory; and (c) clarifying the meaning and implications of universalisation as a principle for guiding the development of disability policies.