Unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is a measure 

of completeness of the Standard Model, and a good tool for looking for its extensions.

In the past few years there have been major new developments in the extraction 

of the CKM matrix elements Vud and Vus from the experimental data. At present, a 

3-sigma unitarity deficit is observed, known as the Cabibbo angle anomaly (CAA). 

I review the main ingredients of CAA across hadronic and nuclear-structure dependent 

radiative corrections, and give an outlook to future developments in theory and experiment.