An overview on studies of the nucleon spin puzzle is given as they
are performed in polarised deep-inelastic lepton-nucleon scattering experiments
and polarised proton-proton collisions. By now, good knowledge is obtained
on the contribution of quark spins to the nucleon spin, while the information
about the gluon contribution is still scarce. Currently, the focus is on the
study of the
orbital angular momentum contribution that is related to the 3-dimensional
structure of the nucleon. It is accessible via generalised parton
distributions that can be measured in exclusive photon and meson production
in lepton
scattering experiments. Here, an active experimental and theoretical program
is ongoing.