  We reconsider the theory of dc and ac interchain conductivity in quasi-one
dimensional systems. Our results are in good agreement with the measured c-axis
optical conductivity of (TMTSF)_2{ClO}_4 and suggest that the c-axis
dc-conductivity of (TMTSF)_2{PF}_6 in the 150K < T < 300Kd$ range is dominated
by precursor effects of Mott localization. The crossover from a Luttinger
liquid at high energy to a Fermi liquid at low energy is also addressed, within
a dynamical mean-field theory. Implications for the inter-chain resistivity and
Drude weight in the Fermi liquid regime are discussed.

Strongly Correlated Electrons