  The scattering theory of quantum transport relates transport properties of
disordered mesoscopic conductors to their transfer matrix $\bbox{T}$. We
introduce a novel approach to the statistics of transport quantities which
expresses the probability distribution of $\bbox{T}$ as a path integral. The
path integal is derived for a model of conductors with broken time reversal
invariance in arbitrary dimensions. It is applied to the
Dorokhov-Mello-Pereyra-Kumar (DMPK) equation which describes
quasi-one-dimensional wires. We use the equivalent channel model whose
probability distribution for the eigenvalues of $\bbox{TT}^{\dagger}$ is
equivalent to the DMPK equation independent of the values of the forward
scattering mean free paths. We find that infinitely strong forward scattering
corresponds to diffusion on the coset space of the transfer matrix group. It is
shown that the saddle point of the path integral corresponds to ballistic
conductors with large conductances. We solve the saddle point equation and
recover random matrix theory from the saddle point approximation to the path
integral.
