  After a brief review of the inclusive and exclusive rare semileptonic decays
of B mesons in the standard model (SM), an overview of recent theoretical
developments in this field is given. New physics effects on various observables
such as branching ratio, backward-forward asymmetry, polarization of lepton and
CP violation in the decays are anlyzed in models beyond SM (supersymmetric
models and two Higgs doublet models).
