In glasses, the largest observed value of nonlinear refractive index n2 is currently about 0.1 X10-11 esu. Changes in n2 are dependent on the third-order electronic polarization, which can be estimated from the linear electronic polarizability or from the refractive index and Abbe number. Theoretical calculations of n2 have been made for some glasses with potentially high nonlinear refractive indexes. Glasses are likewise useful for the matrix of some organic compounds and semiconductors with high optical nonlinearity.