Allelopathy plays an important role in the agroecosystems leading to a wide array of interactions between crop-crop, cropweed and tree-crops. Generally, these interactions are harmful to the receiver plants but provide a selective benefit to the donor. Soil microbes play a key role in determining such interactions as they not only alter the nature of allelopathic interactions but also modify the expression of allelochemicals. Soil sickness problem in the croplands could also be attributed to the allelopathic property or even the autotoxicity. The allelochemicals released largely by the plant residues that are left in the fields after the harvest of crops add to the multifarious problems. If properly managed, these residues could be used for controlling weeds and pests. As is true for any chemical based response, allelopathic interactions are also concentration specific. The promotory functions that are inbuilt need to be worked out and exploited. Now a days allelopathic interactions, in general, and the allelochemicals, in particular, are viewed as an important tool for sustainable weed and pest management, and disease control. In this direction, a number of strate-H. P. Singh is Research Associate, Daizy R. Batish is Reader, and R. K. Kohli is Professor,