The terahertz (THz) radiation generation has seen a very recent development due to the availability of fs optical sources and antenna. THz spectroscopy reveals physical information on the conformational states and low–energy excitations of molecules and solids and potentially enables the study of gas, liquids and solids, water and organic substances, bio-polymers like cellulose, bio-molecules like proteins, amino-acids and DNA/RNA. Among practical application, Thz spectroscopy provides chemical “fingerprint” signature of molecules, Medical diagnostics and security applications, Cultural heritage conservation, Industrial quality control, Tissue/paper imaging.