This thesis considers quality in the National Health Service (NHS), the theories of dialogue, critical systems thinking, and quality - and how these domains can be related together to produce a new concept of quality called critical quality.A quality gap is identified between what the NHS produces and what the public requires of it. It is argued that this gap is unfair because of the generally unequal access of stakeholders to decisions about quality in the NHS. It is suggested that only through dialogue can the gap be reduced in size in a  non-oppressive way.Principles of dialogue are derived from Habermas's (1991a,b) theory of communicative action and applied to interest group relationships using Grant's (1989) insider/outsider model. It is argued that critical systems thinking can be enhanced by embedding interventions within processes of dialogue, and that the analysis of insider/outsider relationships in situations can guide the use of critical systems thinking in creating dialogues.Three modes of quality management are identified (strategic, normative and critical). It is argued that the requirements and needs of the public cannot be met by an NHS that is dominated by strategic and normative quality. Instead critical quality, defined as the specification of services by mediation through dialogue between stakeholders, is advocated as a fairer mode of quality management for the NHS.An NHS quality dialogue (the Trent Quality Initiative) is evaluated. Dialogue is found to have occurred both within and between meetings. Two modes of peer group participation are identified (main dialogue vs meta-dialogue) and two general approaches to the implementation of critical quality in the NHS (incremental vs radical). Finally critical quality in public welfare services is discussed and a research agenda outlined for dialogue, quality and critical systems thinking