A recent survey indicates that a dyadic parent-child approach to art psychotherapy is being used by 60% of British art psychotherapists working with children and young people with some degree of frequency (Taylor Buck, Dent-Brown, & Parry, 2012). However, currently there is insufficient robust evidence to support the efficacy of this approach. Outcome-based studies are needed to demonstrate efficacy, and an important first step in designing such research is to establish an accepted definition of the process and practice of dyadic art psychotherapy. A two-round Delphi process was used to seek consensus on the core therapeutic principles, practices and competences required for the delivery of dyadic art psychotherapy. Consensus was reached on ten principles, six practices and fifteen competences required for the delivery of art psychotherapy which could be used in practice, evaluation and future outcome-based research.