  As the dimensionality is reduced, the world becomes more and more
interesting; novel and fascinating phenomena show up which call for
understanding. Physics in one dimension is a fascinating topic for theory and
experiment: for the former often a simplification, for the latter always a
challenge. Various ways will be demonstrated how one-dimensional structures can
be achieved in reality. In particular organic conductors could establish
themselves as model systems for the investigation of the physics in reduced
dimensions.
  In the metallic state of a one-dimensional solid, Fermi-liquid theory breaks
down and spin and charge degrees of freedom become separated. But the metallic
phase is not stable in one dimension: as the temperature is reduced, the
electronic charge and spin tend to arrange themselves in an ordered fashion due
to strong correlations. The competition of the different interactions is
responsible for which broken-symmetry ground state is eventually realized in a
specific compound and which drives the system towards an insulating state.
  Here we review the various ordering phenomena and how they can be identified
by dielectric and optic measurements.
