We develop the general nonequilibrium theory of transport through a quantum dot, including Coulomb blockade effects via a \(1/N\) expansion, where \(N\) is the number of scattering channels. At lowest order we recover the Landauer formula for the current plus a self-consistent equation for the dot potential. We obtain the leading corrections and compare with earlier approaches. Finally, we show that to leading and to next leading order in \(1/N\) there is no interaction correction to the weak localization, in contrast to previous theories, but consistent with experiments by Huibers et al. [Phys. Rev. Lett. 81, 1917 (1998)], where \(N=4\).