The ATLAS experiment at the Large Hadron Collider has performed accurate measurements of mixing and CP violation in the neutral B mesons, and also of rare processes happening
in electroweak neutral B-mesons decays.
This contribution focuses on the latest
results from ATLAS, including measurements of the branching fractions of $B^0 \to \mu^+ \mu^-$ and $B_s^0 \to \mu^+ \mu^-$ channels and of the CP violation in the $B_s^0 \to J/\psi \phi$ channel.