This special issue – Protecting and sustainably using the world’s plants and fungi – features the research that underpins Kew’s State of the World’s Plants and Fungi 2020 report. This special issue, and the associated report, are global efforts representing work from 210 authors, in 97 institutions, across 42 countries and six continents. We anticipate that this landmark special issue will inform and inspire researchers, policymakers, practitioners and many others to value and appreciate the world’s plant and fungal diversity and its largely untapped potential to help address the global challenges faced by humanity.