Nonlinear optics is a new frontier of science and technology playing a major role in the emerging era of photonics. Photonics involves the application of photons for information and image processing and is branded to be the technology of the 21st century, wherein nonlinear optical (NLO) processes have applications in the vital functions such as frequency conversion and optical switching. These require materials exhibiting second-order NLO effects and hence there is a great need for device quality single crystals. Materials with large second-order nonlinearities, short transparency cut-off wavelengths and stable physicochemical performances are needed in order to realize many of the applications.L-alanine family of crystals are found to promising materials for NLO applications. Most of the chemical analogs of L-alanine exhibit remarkable NLO property. This book briefly explains the nonlinear optical theory, various methods of crystal growth and characterization techniques. Also explains the growth and properties of Alanine complexes namely, L-alaninium oxalate (LAO), L-alaninium maleate (LAM), Mono-L-alaninium nitrate (MAN) and L-alaninium tartrate (LAT) single crystals.