In this chapter, we tackled higher order statistics (HOS) for 2-D signals. In the first part, we recall the definitions of moments and spectra of higher orders as well as their generalization to 2-D signals. We see that the third-order moments as well as the bispectra are 4-D quantities and that the exploitation of the information contained in this structure is found to be difficult. We have to define the structures (projections following given axis) to interpret the bispectral information.