High power radio waves are capable of exciting a variety of parametric plasma instabilities in the ionosphere. Certain instabilities of this type result in the generation of electrostatic plasma waves and plasma density irregularities. These generation processes are often accompanied by strong anomalous absorption of the high power radio waves and this, in turn, gives rise to the large scale modification of the temperature and density of the ionospheric plasma. Results of some recent ionospheric modification experiments undertaken with the Max-Planck Institut fur Aeronomie (Lindau) high power facility at Tromso, Norway, are reviewed. The interpretation of these results in terms of the nonlinear development and saturation of the plasma instabilities involved is also discussed.