The purpose of this paper is to address three major shortcomings of Sen's capability approach with regard to sustainability: (i) First, the weakness of the ecological dimension of the capability framework. This can be overcome by devising a place where it is possible to relate the intrinsic and instrumental values of Nature; (ii) Second, the issue of responsibility, which is only considered from a consequentialist viewpoint by Sen (i.e. ex-post responsibility). Such a restrictive view can be extended by adding the ex-ante dimension of responsibility; (iii) Third, the relationship between the individual and collective levels. This can be overcome by introducing the idea of collective agency. Overcoming these limitations makes it possible to fully integrate the ecological dimension into an extended vision of the capability approach which makes it consistent with strong sustainability, and which leads to a new definition of the agent as a responsible person acting so as to generate sustainable human development.