This thesis proposes a critical, systemic and pluralist approach to evaluating health programs. It examines ways in which efforts to promote equality and plurality are undermined by the application of foundationalist and universal conceptions of social justice and evaluation. This approach is developed within the current debate taking place in the field of Critical Systems Thinking, particularly in the area of the evaluation of social and health programs. It is argued that the potential for equality and plurality in Western societies goes beyond the questions of economic exploitation, military, cultural and political oppression and encompasses the relation between power and knowledge which is inherent in rationalities governing the formulation, the implementation and the operation of health programs. The thesis offers an alternative view of social justice that conciliates equality with plurality, and promotes these values through an evaluative procedure. Using Foucault's philosophy, it is proposed that a nonfoundationalist conception of social justice should be understood in terms of the interactions between three areas of human activity, namely knowledge, morality, and techniques and technologies of government. As regards the possibilities for developing a non-foundational and non-universal evaluative judgement, the thesis assumes a decentered conception of truth in the analysis of society and morality, and acknowledges the role of power as factor of generalisation or diversification of truth. Thus complexes of power-knowledge-morality are at the centre of our evaluative judgements of social justice. In order to encourage equality and plurality, this thesis proposes a rationale for evaluation that includes three main methodological guidelines: a decentered conception of critique regarding the problems and negative effects of a health program (unfolding in reverse); the promotion of subjectivity (autonomy, diversity, solidarity) through self-knowledge and self-regulation of desires (folding); and participation in the reordering of society through an ethical and political process of decision-making (ethical and political unfolding of the situated truths of the subjects). The processes are designed to interrelate and iterate in a complex way. They should include the exploration, choice and combination of methods and/or their parts, and of the strategic positions in scientific and ethical discursivities by thinking critically and acting in a situated and participative way.