Collaboration is strongly promoted as an effective means for cities to respond to climate change. While collaboration is perceived to offer opportunities to progress climate action in cities, little is known about how collaboration can enable low-carbon transformation in practice. Furthermore, while collaboration is largely framed as a positive endeavour, there is a need to more carefully explore the challenges and barriers that may arise. This paper explores the aims, processes, and outcomes of collaboration within urban climate governance. Drawing on a policy review and semi-structured interviews, we present empirical findings from the case study of Hong Kong. This paper identifies three types of collaboration that are structured by regulations, oriented to policy goals, and emerge as everyday practices within the governance of climate change and the energy system. The forms of collaboration challenge the assumptions that collaboration always brings positive outcomes in mobilising action for climate change. While collaboration opens up different modes of governance within cities, the paper highlights significant barriers in terms of the diverse roles of actors, ongoing power imbalances, and shifting governance spaces for intervention. Given the prevailing interest in working together, it is critical to review carefully how collaboration facilitates cities to achieve their climate goals and create momentum for action.