Springer-Verlag Berlin Heidelberg 2010. Cotton plant is the most important source of natural fiber. The plant also provides seeds, linters, and hulls that are used for food, feed, and several other diverse applications. Traditionally, the cultivation of cotton crop has relied heavily on the use of highly toxic pesticides. Because of its susceptibility to a variety of pests and pathogens and the fact that it is a source of several useful products, the cotton plant offers a large number of targets for modification and improvement through genetic engineering. Transgenic cotton, resistant to certain insects and some herbicides, has been accepted enthusiastically by the farmers in many countries, including the United States, China, and India. This chapter describes various methods and tools used to transform cotton, important traits engineered into this plant, and novel possibilities offered for improvement by the recent advances in genetic modification technologies.