In recent days the nanocomposites are grown rapidly, both in their applications and economic importance. This book deals with the synthesis and study of Polypyrrole, Nickel Oxide, Polypyrrole-Nickel Oxide nanocomposite and CSA doped Polypyrrole-Nickel Oxide nanocomposite for NO2 gas recognition. The synthesized sensors were characterized for structural, compositional, morphological, electrical and gas sensing properties. The gas sensing performance was carried out at operating temperature in terms of their response, selectivity and response-recovery time for various oxidizing and reducing gases. The CSA doped Polypyrrole-Nickel Oxide nanocomposite sensors showed enhanced gas sensing performance.