In this article, we present a qualitative study examining students' thoughts and strategies while transferring concepts about energy in physics. We include theoretical approaches of existing transfer research and findings from think-aloud interviews with 20 students of different ages and school levels to develop a framework for analysing the transfer process. The results of both traditional transfer studies and modern approaches, such as the 'Actor-Oriented Transfer perspective' (AOT) and 'Coordination Class Theory' (CCT), are regarded as a theoretical foundation for the framework. Our empirical data involves the statements of students solving a physics task with questions regarding the energy concept, which we used to inductively derive categories for our framework. We conclude that the transfer process is highly individual and that our framework can make this process visible. Knowledge can be transferred with or without a relation to the contextual features of the transfer situation, and it is possible that students describe the context situation itself without relating it to their existing knowledge pieces. Finally, we found four metacognitive strategies that students use while transferring their knowledge. The findings will help teachers to focus on the applicability of knowledge and on practising the use of transfer strategies.