The dynamic behaviour of epithelial tissues plays a central role during development. These processes occur as a result of cell adhesion, migration, division, differentiation and death, and involve multiple processes acting at the cellular and molecular level. In combination with experimental studies, mathematical modelling can help us understand what factors are involved in regulating cell- and tissue-level behaviour. In this talk I describe our recent application of 'cell-based' modelling approaches to understand aspects of epithelial dynamics in several settings, including germ-band extension and tissue size control in Drosophila. I highlight the biological insights gained through this work, as well as ongoing challenges associated with such modelling approaches.