Growth performance is a trait of great economic importance in animal production; it determines the level of breakthrough in animal business. But unfortunately, information on this trait is not readily available to animal scientists, especially small scale farmers, who are more numerically and are striving to contribute to the economic development of nations. It is hoped that this book will bridge the information gap thereby increasing productivity. The performance of animals for any production purpose has been known to be greatly influenced by different environmental factors. Therefore selection of genetically superior animals as parents can only be successful if the influence of such factors can be disentangled. In this book, study was conducted to investigate the effects of genetic and non-genetic factors on growth traits in 595 lambs (306 Balami and 289 Uda). Data collected was analyzed to determine the influence of breed, parity, sex, type of birth, season of birth and year of birth on growth performance traits in Balami and Uda breeds of sheep. Results showed that environmental factors have an important role in expressing of genetic potential in the lambs.