In this paper, landfill is described as bioreactor. Firstly, the bioprocesses taking part within the landfill together with their mathematical descriptions are presented. Secondly, the investigations on various landfill operational procedures are shown. The method which enables the studies on landfill behaviour is also described. Three basic concepts for a landfill design operation are explained: dry landfill, bioreactor landfill and final storage quality landfill. The advantages of landfill operating as bioreactor are stressed.