The dumping of solid waste in uncontrolled landfills can cause significant impacts on the environment and human health. So, the location of landfill is a very important factor that ensures the long working life of landfill. The principle concern is focused on the locational criteria on which the site selection of landfill depends. In this paper the concept of landfill site selection index, a tool for quantifying the suitability of site for landfill construction has been described and its practical application has been demonstrated by comparing the potential of three already existing landfill sites in Delhi namely, Okhla landfill, Ghazipur landfill and Bhalswa landfill. It is observed that all the three existing landfills are in error zones and do not follow the safety criteria for all the factors on which landfill site selection depends.