Rare B Decays in the Standard Model

We discuss the electromagnetic-penguin-dominated radiative B decays $B \to X_s + \gamma, ~B^{\pm (0)} \to K^{*\pm (0)} + \gamma$, and $B_s \to \phi + \gamma$ in the context of the standard model (SM) and their Cabibbo-Kobayashi-Maskawa (CKM)-suppressed counterparts, $B \to X_d + \gamma$, $B^\pm \to \rho^\pm + \gamma, ~B^{0} \to (\rho^{0}, \omega) + \gamma$, and $B_s \to K^{* 0} + \gamma$, using QCD sum rules for the exclusive decays. The importance of these decays in determining the parameters of the CKM matrix is emphasized. The semileptonic decays $B \to X_s \ell^+ \ell^-$ are also discussed in the context of the SM and their role in determining the Wilson coefficients of the effective theory is stressed. Comparison with the existing measurements are made and SM-based predictions for a large number of rare B decays are presented.