In December 2022 the 15th Conference of the Parties to the Convention on Biodiversity agreed a series of measures that requires ‘effective conservation and management’ of 30% of the world’s lands, waters and oceans. Determining where this attention should be directed – the exercise of conservation prioritisation – preoccupies many of the world’s leading conservation scientists. Conservation prioritisation is data hungry. It requires numerous data layers depicting land cover and land cover change, eco-region maps, agricultural activity, human populations, wealth, species distribution, predictions of how all these will change as the climate warms and so on. In this presentation I outline a new way of looking at the challenges of prioritisation by considering the data justice issues that it presents. I outline first why we need to think about data justice, and how it differs from other established concepts like epistemic justice. I then discuss what forms of data are being used in some conservation planning exercises and how using a data justice lens can help us better to understand the challenges they pose. I suggest practical ways of responding to some of the ethical challenges that arise.