The study of leaf expansion began decades ago and has covered the comparison of a wide range of species, genotypes of a same species and environmental conditions or treatments. This has given rise to a large number of potential protocols for today’s leaf development biologists. The final size of the leaf surface of a plant results from the integration of many different processes (which may be quantified by various developmental variables) at different organizational levels, such as, the duration and the rate of leaf production by the plant, the duration and the rate of individual leaf expansion, and also cell production and expansion in the leaf. There is much evidence to suggest that the magnitude of a variable at one organizational scale cannot be inferred to another scale because of different feedbacks from one scale to another. This chapter offers a series of protocols, which are the most commonly used in plant developmental biology, to assess quantitatively leaf expansion both at the scale of the shoot and the individual leaf. The protocols described here are for the comparison of Arabidopsis thaliana genotypes, but can be easily adapted to compare leaf expansion under different environmental conditions and in other dicotyledonous plants.