This document reports the methodology that underpinned the Source to Sea – Zero Pollution 2030 (SOS-ZEROPOL2030) project, which aims to deliver a stakeholder-led zeropollution framework for achieving the European Union’s long-term ambition of ‘Zero
Pollution’ in European seas. This paper introduces the CO-ACT methodology as a transdisciplinary co-creation approach for transformative action that helps define and address urgent and complex environmental problems.