  There is a growing amount of evidence that QCD (and four-dimensional gauge
theories in general) possess a hidden symmetry which does not exhibit itself as
a symmetry of classical Lagrangians but is only revealed on the quantum level.
In this review we consider the scale dependence of local gauge invariant
operators and high-energy (Regge) behavior of scattering amplitudes to explain
that the effective QCD dynamics in both cases is described by completely
integrable systems that prove to be related to the celebrated Heisenberg spin
chain and its generalizations.
