THE STRUCTURE OF THE NUCLEON LONGITUDINAL SPIN

In the last 5 years, the g(1) polarized structure functions of the pro ton, deuton and neutron have been measured very precisely at CERN and SLAC. These new data allowed to confirm experimentally the validity of the Bjorken sum rule relating the quark and gluon structure of the nu cleon to the neutron lifetime. They have also shown that the quarks ca rried only one third of the proton spin. Understanding this result req uires now to measure the gluon polarized structure function. This is t he goal of a new generation of experiments in the next 10 years.