  We study the decoupling transition of flux lattices in a layered
superconductors at which the Josephson coupling J is renormalized to zero. We
identify the order parameter and related correlations; the latter are shown to
decay as a power law in the decoupled phase. Within 2nd order renormalization
group we find that the transition is always continuous, in contrast with
results of the self consistent harmonic approximation. The critical temperature
for weak J is ~1/B, where B is the magnetic field, while for strong J it
is~1/sqrt{B} and is strongly enhanced. We show that renormaliztion group can be
used to evaluate the Josephson plasma frequency and find that for weak J it
is~1/BT^2 in the decoupled phase.
