Adoption of every new technology always involves advantages and risks; Bt cotton is new technology; which in developed countries is well known for many advantages like reduced application of pesticides, better insect pest control and higher lint yield but its success in developing countries still carries a question mark. Global adoption of Bt cotton has risen dramatically from 0.76 million hectares in its introductory period in 1996 to 7.85 million hectares in 2005. This book aims that adoption of Bt cotton may prove to be green revolution in enhancing the cotton yield. Although adoption of Bt cotton is increasing day by day due to its beneficial effects on environment by reduction of pesticide application; however these are some factors responsible for changes in efficiecy of Bt gene and thus in yield of Bt cotton including internal phenology (genetics), environmental changes, nutrition etc.