  We present a detailed discussion of both theoretical and experimental
evidence in favour of the existence of states of ``confined coherence'' in
metals of sufficiently high anisotropy and with sufficiently strong
correlations. The defining property of such a state is that single electron
coherence is confined to lower dimensional subspaces (planes or chains) so that
it is impossible to observe interference effects between histories which
involve electrons moving between these subspaces. The most dramatic
experimental manifestation of such a state is the coexistence of incoherent,
non-metallic transport in one or two directions with coherent transport in at
least one other direction. The magnitude of the Fermi surface warping due to
transverse (inter-subspace) momentum plays the role of an order parameter (in a
state of confined coherence, this order parameter vanishes) and the effect can
occur in a pure system at zero temperature..... ..anomalous transport data in
the (normal state of the) cuprate superconductors and in the low temperature,
metallic state of the highly anisotropic organic conductor (TMTSF)$_2$PF$_6$
cannot be understood within a Fermi liquid framework, and, we argue, the only
plausible way to understand that transport is in terms of a state of confined
coherence.
