The rich phenomenology of internal transport barriers (ITBs)observed in tokamaks includes a poloidal spin-up precursor forbalanced injection neutral beam heating and stepwise expansion of thebarrier for unbalanced injection. Examples of numerical simulations ofthese phenomena are presented. Two drift wave based predictivetransport models (GLF23 and multimode) are used. Both models includethe suppression of ion temperature gradient modes as the E × B shearapproaches the computed maximum linear growth rate. Modelling ofdischarges with ITBs from the DIII-D, JET andTFTR tokamaks are compared.