Book excerpt: Allelopathy offers great potential: (a) to increase agriculture production (food grains, vegetables, fruits, forestry), (b) to decrease harmful effects of modern agricultural practices (multiple cropping, leaching losses from N – fertilizers, indiscriminate use of pesticides viz. weedicides, fungicides, insecticides and nematicides and development of pesticides tolerant /resistant biotypes in pests) on soil health/productivity and on environment and (c) to maintain soil productivity and pollution free environment for our future generations. It is hoped that in the near future the allelopathy may be used in crop production, crop protection, agroforestry and agro-horticultural systems of developed countries. Therefore, it may be one of the strategies to increase agricultural production in Sustainable Agriculture of 21st century. This book is based on the research findings and addresses to various intricate problems of crop production, to which there was no definite answer in the past but now have been attributed to allelopathy.