Numerous experiments were performed on JET to clarify the link between rational q, magnetic shear and ITBs, by producing Internal Transport Barriers (ITBs) in plasmas with various q-profiles. A reconstruction of the plasma equilibrium using the EFIT code with motional stark effect (MSE) and polarimetry constraints was verified by analysing MHD activity. Modelling of transport properties of plasmas produced in the experiment was done using the TRANSP (transport analysis), JETTO (predictive transport-micro-stability) and TRB (turbulent transport) codes. Two types of ITBs were analysed corresponding to different q-profile shapes: ITBs in a region of negative magnetic shear (s<0) and ITBs in the vicinity of rational q surfaces. Different models were used for the calculating the linear growth rate of micro instabilities. Calculated transport coefficients predicted by theory were compared with data deduced from the experiment.