  The determinations of the Cabibbo angle from kaon, pion, $D$ and tau decays
disagree with the one from super-allowed beta decays. The resulting $\approx
3\,\sigma$ deficit in first row (but also first column) CKM unitarity is known
as the Cabibbo angle anomaly (CAA). Determining $V_{ud}$ from beta decays
requires knowledge of the Fermi constant $G_F$, usually extracted from muon
decay. However, because new physics might also affect muon decay, and thus the
determination of the Fermi constant, an interesting interplay with the global
electroweak fit arises where $G_F$ is a crucial input. In these proceedings we
review the CAA and its different interpretations in terms of physics beyond the
SM, first discussing the corresponding effect in the effective field theory and
then using (simplified) models.
