The present book is aimed towards the development of NLO single crystals of p-Toluidine p-Toluenesulfonate, L-Proline Succinate, L-Arginine semicarbazide and L-lysine sulphate are exhibiting NLO property more than that of KDP, and these grown materials can be used as a better replacement for KDP to find applications in the field of opto-electronics. These crystals belong to the amino acid group, which exhibit the nonlinear optical (NLO) property remarkably. The characterization studies include single XRD analysis, UV analysis, mechanical and dielectric studies of the grown crystals. The dielectric and photoconductivity measurement were also carried out for the grown crystals to probe the nature of the conductivity. Hence, the grown crystals are to be confirmed for the single crystalline nature using XRD technique. From UV spectral analysis the required transmission range for the Second Harmonic Generation (SHG) and optical band gap have been estimated.The mechanical, dielectric, and photoconductivity studies were carried out to probe the mechanical strength and polarizability nature of the grown crystals.