  The gauge invariant operator formulation of the angular momentum sum rule
${1\over2} = J_q + J_g$ for the proton is presented and contrasted with the sum
rule for the first moment of the polarised structure function $g_1^p$. The
decoupling of the axial charge $a^0$ from the angular momentum sum rule is
highlighted and the possible QCD field-theoretic basis for an angular momentum
sum rule of the form ${1\over2} = {1\over2}\D q + \D g + L_q + L_g$ is
critically discussed.
