Revision of the National Mediator Accreditation System, effective from 1 July 2015, removes the requirement for mediators to demonstrate understanding of neutrality as an ethical competency. The principle of impartiality has been retained and the principle of self-determination has been newly included as an ethical competency. The self-determination of participants, recognised in the original version of the NMAS, has been more clearly articulated as the aim of mediation practice. Abandonment of the principle of neutrality signals a need to reconsider the role of the mediator, which was once identified with control of the process of mediation, though neutral as to its content and outcome. Abandonment of neutrality calls for an alternative frame of reference for ethical practice in mediation. In this paper, the relationship of trust between mediator and parties is proposed as a suitable and defensible alternative ethical framework. It is argued that this relationship can be constructed according to principles associated with fiduciary and therapeutic relationships, in recognition of the distinctive socio-legal context of practice. Abandonment of neutrality also raises issues as to the mediator’s role in achieving fairness for participants. It is argued that relationships of trust provide a convincing framework within which to consider issues of substantive fairness in mediation.