This book will helpful to academic, student, reserchers to understand gene action and concept of heterosis of QPM. QPM is a bio-fortified maize with increased lysine and tryptophan level. lysine is the first limiting amino acid followed by tryptohan and threonine in the diet of non-ruminent and human. Gene action or combining ability analysis is a one of the most powerful tool in identifying the best combiners that may be used in crosses either to exploit heterosis or to accumulate productive genes. Heterosis is the one of the greatest practical contribution of genetics and it has most significant expression in maize crop. In view of the above facts and in order to develop productive and industrially important quality protein maize hybrids, the present investigation was undertaken by using Line x Tester mating design to derive information on the various genetic parameters.