Dimuon decays and rare B decays prospects from CMS

$B$ hadrons are an ideal tool for advancing our current understanding of the flavour sector of the Standard Model (SM), and searching for effects originating from physics beyond the SM, thanks to the large production rate and the fact that $B$ hadrons are relatively easy to trigger on and identify due to their long lifetime and high mass. In this talk, first CMS results on dimuons at proton-proton collisions at $\sqrt{s}=7$ TeV are presented, and CMS prospects for the rare decay $B^0_s \rightarrow \mu^+\mu^- $ are reviewed.