The International Baccalaureate (IB) was introduced to Australia 40 years ago, and still occupies a contested place within the Australian educational landscape. With IB programmes now present in over 190 schools across all states, territories, and sectors, questions remain about its practical role and purpose within Australia’s national policy architecture. Critical studies to date have explored its holistic curriculum and inquiry-based pedagogy, its language acquisition priority, and its commitment to an inclusive humanistic anthropology. Broader questions have been raised, however, concerning its perceived privileging of Western epistemology, its socio-educational inaccessibility, and whether these combine to serve neo-liberal globalisation goals contrary to the IB mission statement. The voices of those who lead Australian IB schools, the principals, have thus far been silent. Given the centrality of the principal in schools, this silence is striking. This presentation reports on the first focused study to be undertaken of principalship in Australian IB schools. It explores how Australian principals perceive the presence of the IB in their school impacts their experience of leadership. Using a mixed methods approach, seven principals from across three states were interviewed in Phase One. The total population of Australian IB school principals were then invited to participate in a survey based on findings from Phase One interviews. The theoretical framework guiding the study was derived from complexity leadership theory.A series of tensions for principals are identified. These include competing curriculum obligations, duality of pedagogical cultures, unity of governance and community expectations, and socio-educational dissonance. Principals who actively embrace temporal, relational and cultural concepts of agency are considered more effective in leading the contextual ambidexterity evident in Australian IB schools.