The coexistence of fusion plasmas with the material walls surrounding it and their interaction has many destructive consequences both for the walls and for the plasma. Plasma wall interaction (PWI) is, however, a necessary ingredient of fusion plasmas on the earth. This contribution addresses the main PWI processes by which impurities are released from the walls. Following this redeposition of eroded material and local material transport is discussed. Finally wall conditioning will be discussed which offers the possibility to control some of the plasma wall interaction processes.