The description of order in mesophases in terms of angularly dependent radial distribution functions and in terms of correlation functions in density and oreientation is discussed. The determination of these functions from light scattering and diffraction data is described. The concept of non-randomness of orientation correlations is introduced and its description in terms of non-randomness parameters or correlation functions isn proposed. It is pointed out that mesophases of complex structure may be defined in terms of parameters describing the amplitudes and correlation distances for the correlations in density and in random and non-random orientation. The most striking chages at mesophase transitions are in the randomness of the orientation correlations. The relationship between the correlation functions and the morphology for model systems is illustrated.