The present book focuses on the development of metal oxide heterostructured nanocomposite based gas sensors using simple and low-cost co-precipitation and sol-gel processes. The main focus is emphasized on the synthesis of metal oxide nanocomposites using SnO2/Fe2O3, NiO/CeO2, NiO/SnO2, CeO2/Fe2O3, and ZnO/NiO. A systematic characterization of prepared nanocomposites for their structural, morphological, microstructural, and compositional studies is done. Gas sensing properties of the fabricated sensors towards various reducing gases were studied. SnO2/Fe2O3 core-shell sensor has shown tremendous response towards 2-methoxyethanol at room temperature. NiO/SnO2 and CeO2-Fe2O3 sensors have shown enhanced sensing properties towards ethanol at room temperature. NiO/CeO2 and ZnO/NiO sensors have shown superior sensing response towards isopropanol and ammonia respectively at room temperature. The heterostructure is the main contributor for these enhanced sensing properties of composite sensors over their pure counterpart based sensors.