Cotton is the major textile fibre used by man. Pakistan stands fourth among ten top cotton- producing countries in the world. Cotton being the major crop of earning foreign exchange, it needs more care than other crops for realization of high yield. It is evident from the fact that Pakistan has low per hac seedcotton production. Cotton is principal component of Pakistan’s economy owing to its 69% share in foreign exchange earning, 7.5% value added in agriculture and 1.6% in GDP. Cotton is sixth largest source of vegetable oil in world, however, in Pakistan its share is 70% in local edible oil industry.In this book I will share the knowledge regarding the combining ability, heterosis, gene action, correlations and genotype x environment interaction among quantitative and quality traits.