The study introduces a theoretically and methodologically novel approach to study the development of expertise in life sciences by combining a longitudinal perspective with case and intervention approaches. The development of expertise requires processes at different levels: a domain-specific conceptual understanding, conceptual change, knowledge integration and understanding of the relationship between theoretical knowledge and practical skills. However, there is little empirical data showing the interaction between these approaches, while the role of conceptual change has been almost neglected in higher education. In this multi-method study, bridges will be created between these research traditions. The results of the CELLS project will open up new theoretical perspectives and empirical evidence in this little investigated, though promising, research avenue related to the interaction of theory and practice in the development of expertise.