  We give a gauge-invariant treatment of the angular momentum sum-rule for the
proton in terms of matrix elements of three gauge-invariant, local composite
operators. These matrix elements are decomposed into three independent form
factors, one of which is the flavour singlet axial charge. The other two are
interpreted as total quark and gluon angular momentum. We further show that the
axial charge cancels out of the sum-rule. The general form of the
renormalisation mixing of the three operators is written down and also
determined to one loop from which the scale dependence and mixing of the form
factors is derived. We relate these results to a previous parton model
calculation by defining the parton model quantities in terms of the three form
factors. We also mention how the form factors can be measured in experiments.
