The Co-creation Playbook provides practical tools for co-creation of behavioral interventions and nudges, ensuring that the interventions are relevant, accessible to target groups and ethically sound. As an example, it explores interventions that have already been tested to promote public transport and their effectiveness, and describes the co-creation process carried out in the 1.5 Degree City project, funded by the NetZeroCities programme. The Nudge Playbook is based on a literature review, Turku region public transportation survey data, our experiences from co-creation workshops, and information about interventions from Nordic Cities.