A review of measurement techniques and nonlinear coefficient values are presented. Coefficients of a few materials are evolving as standards by consensus based on independent measurements. Improved instrumentation, extension of measurement techniques, and more detailed analysis are improving accuracy in recent measurements. Confusion still remains for values of some materials, and specification of the reporting frame for the tensor values remains an issue.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.