Flavor Physics with CMS at LHC

The investigation of heavy flavor physics represents an alternative approach to direct New Physics searches at LHC. The CMS experiment concentrates its effort on decays with muons in the final state, that can be efficiently selected by the multiple-level triggers. We summarize here the perspective and expected results on different processes, from rare beauty hadron decays, $\tau$ decays and $q {\bar q}$ production, using data which will be collected in the first years of LHC running.