Image formation processes of LEEM and PEEM are described in detail. This study is important in understanding the surface processes by use of such microscopes. LEEM images can be understood by the diffraction and interference contrast. The latter can be classified into geometric phase and quantum size contrast. The LEED patterns that are obtained with LEEM optics are different from those observed with the conventional LEED optics. This characteristic should be taken into consideration in the analysis of LEED patterns in LEEM optics. The future trend in LEEM and PEEM is also described. Improvement of the lateral resolution is being made by adopting the mirror corrector and the new image processing method.