The article presents experimental and theoretical investigations on thedynamics of sawteeth and neoclassical tearing modes in tokamakplasmas. The main findings of these investigations are: (1) Theexperimental validation, on the basis of FTU and TCV data, of a model for the prediction of the sawtooth period and amplitude; (2) the importance of diamagnetic effects in determining the threshold for sawtoothcrashes and the rotation of non-linear tearing modes; (3) a clarification of collisionless reconnection processes, in particular the role of phase mixing in association with magnetic island growth and saturation in dissipationless regimes. The interplay between ECRH and macroscopic island dynamics is alsodiscussed.