With the EMC experiment in the late 1980s which showed the quark spin
to have a very small contribution to the proton spin, the hunt has
been on for other sources. I focus on the angular momentum
contribution generated by the motion of quarks and gluons inside the
proton. The Generalised Parton Distributions play a key role in our
understanding of this study. By making a connection to helicity
amplitudes we can have a physical motivation for the OAM picture
described by the GPDs. Most importantly, it helps us understand how we
can connect orbital angular momentum to an observable that can be
measured experimentally.
