We describe the properties of the strongly interacting 2-D electron gas in high magnetic fields whose properties can be described in terms of the formation of composite fermions at fractional Landau level occupancy. For a Landau level occupancy v = 1 the excitations correspond to spin waves for high g-factors and magnetic fields, but when the g-factor is reduced close to zero by the use of hydrostatic pressure, there is strong evidence for the formation of Skyrmions. Studies of the composite ...