For simulations of electron images, the Bloch wave approach is more convenient for dealing with these cases in which either the crystal contains no defects or the image resolution is so low that the column approximation holds. When the image resolution approaches the atomic level, the dominant contrast mechanism is phase contrast, and the effect of diffraction contrast is minimized. In this case, it is more convenient to apply the multislice theory, particularly when defects are present in the crystal. The most important advantage of the multislice theory is that it does not require three-dimensional periodicity of the crystal; thus images of interfaces, surfaces, and dislocations can be simulated. In this chapter outlines the theoretical scheme of the multislice theory and its applications. Methods to improve the theory are illustrated to include HOLZ reflections accurately.