Biological Nitrogen Fixation (BNF) and contribution to ecosystem by legumes has received a significant reviewed by researchers in the 21st century, with more priority given to soybeans and cowpeas. Little is known about the BNF potentials of groundnut (Arachis hypogaea L)and also the variability existing among its cultivated lines as well as their possible response to added amendment and environmental stress such as moisture and temperature.It is important to note that, the mere existence of legumes in the soil does not translate to efficient BNF,but will depends on the crop residue management adopted by the farmer which will influence the soil nitrogen balance sheet, and subsequent contributions to the following non-legume crop grown after it. Hence, this book is a handy document intended to bridge such gap. The book centered on two major themes: (a)Symbiotic nitrogen fixation by groundnut (Arachis hypogaea) genotypes and nodulation as influence by starter inorganic nitrogen fertilizer and (b)Nitrogen contribution by groundnut genotypes to soil Nitrogen Balance. Interesting fact about the two sub themes are extensively discussed.