Oceanic islands contribute disproportionately to global biodiversity and harbor a high number of endemic species that exhibit unique evolutionary and functional adaptations, shaped by their life in isolation. Owing to their exceptional endemism and diversity, high vulnerability to multiple global change drivers, and under-representation in many global biodiversity databases and initiatives, oceanic islands are a top priority for assessing the status and monitoring the trends of biodiversity. Thus, in BioMonI, we will provide unique insights into past, present, and future trends of plant-related essential biodiversity variables and essential ecosystem function variables by leveraging long-term paleoecological archives, vegetation monitoring plots, remote sensing, and modeling of future scenarios. Our goal is to uncover trends in biodiversity across elusive dimensions, expanding the scope of conservation and monitoring efforts by incorporating evolutionary and functional perspectives, as well as biotic associations. We will develop a harmonized monitoring scheme specifically tailored to the challenges of island biodiversity, assemble BioMonI-PLOT – a unique vegetation plot network of oceanic islands, and foster the BioMonI e-infrastructure – making information across archipelagos easily accessible for stakeholders including researchers, citizen scientists, conservation managers, (non-)governmental organizations and public institutions.