  We analyse how $U(3)^5$ and $U(2)^5$ flavour symmetries act on the Standard
Model Effective Field Theory, providing an organising principle to classify the
large number of dimension-six operators involving fermion fields. A detailed
counting of such operators, at different order in the breaking terms of both
these symmetries, is presented. A brief discussion about possible deviations
from these two reference cases, and a simple example of the usefulness of this
classification scheme for high-$p_T$ analyses at the LHC, are also presented.
