The book deals the growth and characterization of four promising NLO active metallo organic crystals namely, ATMB, CMTWMP, CMTG and MMTG. It Explains fundamentals of nonlinear optics (NLO), its importance and the role of NLO materials in the fast changing science and technology. In addition, the background of various methods of crystal growth technique are explained. Literature survey on different types of NLO crystals with specific references to the complexes of thiourea, thiocyanate and allylthiourea and their properties also presented. Also explains the various tools and techniques employed for characterizing the NLO crystals. Further It deals with the growth of tri-Allylthiourea mercury bromide (ATMB), Diaquatetrakis thiocyanato cobalt (II) mercury (II) N-methyl-2-pyrolidone (CMTWMP), cadmium mercury thiocyanate glycol monomethyl ether (CMTG) and manganese mercury thiocyanate glycol monomethyl ether (MMTG) single crystals using slow evaporation technique. The important properties of these crystals such as structural, optical, thermal, luminescence, mechanical, dielectric, photoconductivity, ac & dc conductivity are discussed in detail.