PHYSICS WITH POLARISED PROTONS AT HERA

We discuss some topics on the physics case for using polarised protons and electrons at the ep collider HERA. We show that if a polarisation of 70% can be achieved for the protons, important and partly unique measurements can be made at HERA. These include measurements of the polarised structure function g₁(x) at low x, the polarised gluon distribution in the range 0.001 < x < 0.1, weak asymmetries from charged current events and possible access to polarised parton distributions in the photon. Thus HERA can make a significant contribution to the spin physics program.