This article discusses the use of scientific and Aboriginal knowledge in planning, exploring how their uses are limited within the neo-liberal ideology that underpins planning institutions globally. Western knowledge, based on a scientific, enlightenment philosophy, is often seen as the objective basis for planning and policy-making. However, a more social constructivist view reveals that the use of science in planning is complex; science can be used to justify a neo-liberal agenda, limiting efforts towards sustainability. Aboriginal knowledge, underpinned by an ancestral responsibility, holds an intrinsic obligation for Aboriginal Peoples to care for Country. This knowledge is commonly excluded from planning processes and continually fails to challenge unsustainable neo-liberal planning. We investigate how the neo-liberal ideology limits the uses of these knowledges, contributing to growth and development that risk breaching ecological limits. Drawing on insights from two different research projects, the article shows how politicisation of Western scientific knowledge and the colonisation of Aboriginal knowledge limit plurality and inclusion in planning. We argue that unsustainable planning practice should be challenged through co-learning in order to improve planning. We conclude with suggestions on how a shared understanding of knowledge might be theorised to provoke a sustainable agenda for planning policy and practice.