This issue will focus on STEM & Open Schooling for Sustainability Education. On May 11-12, 2023, the fourth edition of the successful conference series is to take place at https://www.naturalis.nl/en. in Leiden, Netherlands. We call upon all interested researchers, policy-makers and practitioners to join us in this international event dedicated to discuss, experience and co-create PD, open schooling and sustainability education. We invite you to contribute your work, ideas and experiences through one of the featured innovative formats for sharing ideas and for co-creation. Please consult the call for proposals for more detail on these formats and for general organizational information. The conference is brought to you by Naturalis and Utrecht University in collaboration with ICSE and the European H2020 funded project https://icse.eu/international-projects/most/.