Stakeholder involvement and transparency are strongly interrelated. Stakeholder involvement is key to strengthening transparency, while transparency is necessary for effective stakeholder involvement. International and European legal requirements in environmental decision-making, radiation protection, nuclear safety and emergency preparedness and response call for increasing levels of transparency and stakeholder engagement. However, recent nuclear or radiological events demonstrate that transparency and engagement in practice are perceived differently by authorities, media and the public. Research conducted in this study by means of a questionnaire sent to authorities responsible for nuclear/radiological emergency management shows a range of challenges related to transparency during a nuclear or radiological emergency, e.g. fear of panic or timely and proper information. Few countries use the full potential of tools and methods for stakeholder engagement in emergency preparedness, although these may also contribute to improved transparency. Despite lessons learned to enhance transparency and stakeholder engagement in nuclear or radiological emergency management, there is room for improvement at a practical level and for finding a common understanding among stakeholders.