Using a theoretical framework based on the next-to-leading order QCD-improved effective Hamiltonian and a factorization Ansatz for the hadronic matrix elements of the four-quark operators, we reassess branching fractions in two-body non-leptonic decays B → P P, P V, V V , involving the lowest lying light pseudoscalar (P) and vector (V) mesons in the standard model. We work out the parametric dependence of the decay rates making use of the currently available information on the weak mixing matrix elements, form factors, decay constants and quark masses. Using the sensitivity of the decay rates on the effective number of colors, N c , as a criterion of theoretical predictivity, we classify all the current-current (tree) and penguin transitions in five different classes. The recently measured charmless two-body B → P P decays (

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Under two different scenarios for the light scalar mesons, we investigate the transition form factors of B(B s ) mesons decay into a scalar meson in the perturbative QCD approach. In the large recoiling region, the form factors are dominated by the short-distance dynamics and can be calculated using perturbation theory. We adopt the dipole parametrization to recast the q 2 dependence of the form factors. Since the decay constants defined by the scalar current are large, our predictions on the B → S form factors are much larger than the B → P transitions, especially in the second scenario. Contributions from various light-cone distribution amplitudes (LCDAs) are elaborated and we find that the twist-3 LCDAs provide more than a half contributions to the form factors. The two terms of the twist-2 LCDAs give destructive contributions in the first scenario while they give constructive contributions in the second scenario. With the form factors, we also predict the decay width and branching ratios of the semileptonic B → Slν and B → Sl + l − decays. The branching ratios of B → Slν channels are found to have the order of 10 −4 while those of B → Sl + l − have the order of 10 −7 . These predictions can be tested by the future experiments.