  Canonical formulation of quantum field theory on the Light Front (LF) is
reviewed. The problem of constructing the LF Hamiltonian which gives the theory
equivalent to original Lorentz and gauge invariant one is considered. We
describe possible ways of solving this problem: (a) the limiting transition
from the equal-time Hamiltonian in a fastly moving Lorentz frame to LF
Hamiltonian, (b) the direct comparison of LF perturbation theory in coupling
constant and usual Lorentz-covariant Feynman perturbation theory. Gauge
invariant regularization of LF Hamiltonian via introducing a lattice in
transverse coordinates and imposing periodic boundary conditions in LF
coordinate $x^-$ for gauge fields on the interval $|x^-|< L$ is considered. We
find that LF canonical formalism for this regularization avoid usual most
complicated constraints connecting zero and nonzero modes of gauge fields.
