A short literature review shows that a lot of information is available concerning the biological processes that take place in sanitary landfill sites. Although there are still many unknown interactions and phenomena this information could be used to modify the conventional landfill operation technique so that methane production is enhanced. Results from research projects are presented, showing effects of landfill operation on the leachate quality with time. Laboratory scale experiments in which shredded municipal solid waste is anaerobically decomposed under optimum conditions give additional information concerning the reasons for enhancement or inhibition of the biological processes. Proposals for modified landfill operation techniques are presented.