  I revue the so called Wilson loop approach to bound state problem in QCD. I
shall show how using appropriate path integral representations for the quark
propagator in an external field it is possible to obtain corresponding path
integral representations for various types of gauge invariant Green functions
which have the important feature of involving the gauge field only trough
Wilson loop correlators or their generalizations. Two different kinds of
representations are used, one given in the form of a semi-relativistic
expansion, the second completely relativistic of the Feynmann-Schwinger type.
In this way starting from reasonable ansatz on the non perturbative part of the
Wilson correlator one can obtain: expressions for the semi relativistic (spin
dependent and momentum dependent) q \bar q and 3q potentials, a ``second
order'' q \bar q Bethe-Salpeter equation and and a related Dyson-Schwinger
equation. I shall concentrate on the three quark potential for which new
controversial results have been obtained by lattice numerical simulations and
on a three dimensional reduction of the BS equation obtained in the form of the
eigenvalue equation of of a squared or a usual mass operator. We shall report
on a numerical resolution of such equations which seems to give a comprehensive
reproduction of the entire meson spectrum with the exception of light
pseudo-scalar bound states for which a complete four dimensional treatment
should be necessary.
