Pulsars are rapidly rotating neutron stars with ultra strong magnetic fields of the order 10^12 Gauss. The radio emission is believed to originate from deep within their co-rotating magnetospheres, directly above the magnetic poles. Since their discovery, significant progress has been made in our understanding of the emission mechanism of these laboratories of extreme physics. There are two well established models which will be discussed in this talk. The first model explains many aspects of the observed periodic variability in the shape of individual pulses in terms of short-timescale dynamical processes in the magnetosphere. The second model successfully explains the observed position angle (PA) of the linear polarisation by linking the PA to the dipole geometry of the magnetic field. Since the dipole field cannot be expected to change on short timescales, the PA should be stable from pulse to pulse. However, for at least a small number of pulsars the PA is seen to periodically change in tandem with the variability in their pulse shapes. This behaviour is incompatible with the two well established models. By characterising this phenomenon in detail, it is hoped that the various models aiming to explain these complex dynamical processes taking place in pulsar magnetospheres can be further constrained.