In this paper, various types of so-called edge localized mode (ELM), an MHD instability occurring in the edge of H-mode plasmas, are discussed. A phenomenological classification based on experimental observations from several experiments is given. ELMs affect the confinement of both energy and particles, with a stronger degradation of particle confinement. Thus, ELMs provide particle control in the H-mode, allowing steady-state operation at only modest confinement degradation. However, large ELMs may lead to unacceptable power loads on the divertor plates of future large fusion experiments and, thus, active control of ELM type and characteristics is required. At present, three control schemes have been demonstrated, namely dynamic variation of the plasma shape, application of resonant magnetic perturbations and control of the energy flux through the separatrix by additional radiation.