  Light-cone quantization of gauge theories is discussed from two perspectives:
as a calculational tool for representing hadrons as QCD bound-states of
relativistic quarks and gluons, and as a novel method for simulating quantum
field theory on a computer. A general non-perturbative method for numerically
solving quantum field theories, `discretized light-cone quantization', is
outlined. Both the bound-state spectrum and the corresponding relativistic
wavefunctions can be obtained by matrix diagonalization and related techniques.
Emphasis is put on the construction of the light-cone Fock basis and on how to
reduce the many-body problem to an effective Hamiltonian. The usual divergences
are avoided by cut-offs and subsequently removed by the renormalization group.
For the first time, this programme is carried out within a Hamiltonian
approach, from the beginning to the end. Starting with the QCD-Lagrangian, a
regularized effective interaction is derived and renormalized, ending up with
an almost solvable integral equation.Its eigenvalues yield the mass spectrum of
physical mesons, its eigenfunctions yield their wavefunctions including the
higher Fock-space components. An approximate but analytic mass formula is
derived for all physical mesons.
