  A short review of correlated electrons in molecular systems has been
performed. Main attention has been focussed on ET salts, which are the d=2
systems. They show the Mott transition in high temperatures and the transition
from the antiferromagnetic to the superconducting phase in low temperatures,
under a (chemical) pressure. Physical properties (the electrical resistivity,
the specific heat, the magnetic susceptibility, the photoemission spectra, the
optical conductivity) of ET salts have been compared with those ones in other
strongly correlated systems. The optical conductivity is described in the
framework of the Hubbard model, with a low frequency peak as an evidence for
the Abrikosov-Suhl resonance.
