Standard agent and action-based approaches in computer ethics tend to have difficulty dealing with complex systems-level issues such as the digital divide and globalisation. This paper argues for a value-based agenda to complement traditional approaches in computer ethics, and that one value-based approach well-suited to technological domains can be found in capability theory. Capability approaches have recently become influential in a number of fields with an ethical or policy dimension, but have not so far been applied in computer ethics. The paper introduces two major versions of the theory – those advanced by Amartya Sen and Martha Nussbaum – and argues that they offer potentially valuable conceptual tools for computer ethics. By developing a theory of value based on core human functionalities and the capabilities (powers, freedoms) required to realise them, capability theory is shown to have a number of potential benefits that complement standard ethical theory, opening up new approaches to analysis and providing a framework that incorporates a justice as well as an ethics dimension. The underlying functionalism of capability theory is seen to be particularly appropriate to technology ethics, enabling the integration of normative and descriptive analysis of technology in terms of human needs and values. The paper concludes by considering some criticisms of the theory and directions for further development.