Abstract: To-date little research has examined visioning as a practice, including its theoretical underpinnings. In particular, published cases tend to tell high-level positive ‘stories’ rather than consider the tensions and challenges that must be negotiated during a visioning process and that can constrain the impacts of a visioning exercise. In contrast, this paper presents a critical reflection on two visioning exercises run as part of the Visions and Pathways 2040 project – which is funded by the Cooperative Research Centre for Low Carbon Living – focussed on the key tensions and process challenges that were faced and how we attempted to address them. We identify seven main tensions/process challenges, describe how they manifested during the design and convening of the exercises, and evaluate the strengths and weakness of specific strategies that were used to address them. Whilst strong claims of generalisability are not made, the identified tensions/process challenges and strategies are likely to be of relevance to others convening visioning exercises in urban contexts. Five underlying themes are also identified that visioning practitioners need to be aware of, particularly in urban contexts: (i) the complexity and normativity challenges inherent to envisioning new urban systems and low-carbon transitions; (ii) the barriers to systemic thinking and related process design considerations; (iii) the strong barriers to original or breakthrough ideas; (iv) the need for technical or specialised knowledge and to equip workshop participants, whilst being aware of the limitations of experts; and (v) interactivity challenges (involving stakeholders in the research process).