The random-variable formalism of anomalous diffusion processes is presented. We elucidate the role of the subordinate stochastic processes as the main mathematical tool that allows us to modify the dynamics of the classical, exponential relaxation process. In particular, we discuss the anomalous diffusion schemes underlying the stretched exponential decay of modes.

PACS numbers: 02.50.--r, 05.40.Fb, 61.20.Lc