The strong focus in climate negotiations on the transfer and diffusion of technologies as ameans to mitigate and adapt to climate change has entailed various programs to promote the transfer and diffusion of climate technologies, including the Technology Needs Assessment project (TNA). Despite the technology focus in the project, practice shows that the questions of what a technology is and how the key concepts of technology transfer and diffusion should be understood and operationalized remain diffuse. This paper explores the reasons for this by analysing the experience of the TNA project in using a framework for categorizing technologies according to the types of markets and non-markets in which they are diffused. While the framework has contributed to a higher degree of ‘market literacy’ among national stakeholders, four challenges in categorizing technologies have been identified: i) technologies comprising varying degrees of software, orgware and hardware; ii) technologies appearing as whole systems of production; iii) technologies covering different application markets; and iv) technologies situated on a continuum between research, development and diffusion. These challenges are proxies for the challenges in formulating plans of actions for technologies. If, due to a lack of conceptual clarity, it is not clear to countries whether the diffusion of a specific technology should be implemented by a project or by means of an enabling framework, the measures proposed in the action plans may be misleading. We therefore call for an increased focus on clarifying the technology concept in the training for the next generation of TNAs.