  We briefly review some basic aspects of transport in clean metals focusing on
the role of electron-electron interactions and neglecting the effects of
impurities, phonons and interband transitions. Both for small Fermi surfaces of
two and three-dimensional metals and open Fermi surfaces of quasi
one-dimensional metals the dc conductivity sigma is largely dominated by
momentum and pseudo-momentum conservation, respectively. In general, the
frequency and temperature dependencies of sigma(w,T) have very little in
common. For small Fermi surfaces in three dimensions we find for example that
the scattering rate is quadratic in frequency, Gamma \propto w^2, even in the
absence of a T^2 contribution.
