Scanning Electron Microscopes (SEMs) have been used for various applications, such as research and development and failure analysis. There are many cases where not only observation of a specimen surface – but also observation of a cross section – is important. Preparation of a cross section depends on the specimen structure, observation purpose, and materials. Various preparation methods are put into practice: cutting, mechanical polishing, microtome, and FIB (Focused Ion Beam) are the major methods. In this discussion, we evaluate a new cross section specimen preparation method using an argon ion beam (hereinafter called the Cross-section Polishing or CP method). We have found that this method is extremely useful for observation of layer structures, interfaces, and crystalline structures of metals, ceramics, and composites. Here, we introduce examples of applications to various types of specimens.