On the eve of LHC start-up, the main opportunities offered to CMS to discover and ultimately study new physics with $\tau's$ in the final states are presented. From the discovery of the Higgs boson in the Standard Model, of its extension in the MSSM or in non-SUSY alternatives to the measurement of SUSY mass spectrum in $\tilde{q} \to q\tilde{chi}_2^0 \to q\tau\tilde{tau}$ cascade decays, this talk reviews the most recent analyses developed in the CMS collaboration for the low luminosity 21.10^{33}cm^{−2}s^{−1} running phase of the LHC.