Proton Spin, Sum Rules, QCD and Higher Twist

We examine the present status of the Bjorken sum rule in the light of recent data on the spin structure functions of the proton, neutron and deuteron obtained by the CERN and SLAC experimental groups. We also discuss the role of possible higher-twist contributions and higher-order PQCD corrections and comment on the extraction of the necessary parameters, D and F, obtained from hyperon semi-leptonic decays.