Publisher Summary Cytological methods are effective during the period of virus multiplication after the initial infection has become well established. Phase optics allows sequential studies of living cells during virus multiplication. Microspectrographic equipment with appropriate optics, radioactive tracers, and fluorescence microscopy are made possible the examination of most stages in the multiplication cycle. In most instances, advances in knowledge of plant virus cytology are due to the use in combination of two or more techniques or forms of optical equipment. This chapter discusses the microscopic techniques confined to phase and bright light microscopy, Ultraviolet (UV) microspectrophotometric methods, and their application to virus-infected cells. The selection of normal and infected cells for examination and similar problems are discussed in this chapter. Possibly the nucleolus-to-cytoplasm sequence is common in the synthesis of many plant viruses, but it need not be invariable. Supposing the final act of infection was due to the RNA of a single virus particle finding an appropriate site in the nucleolus. A limitation in the use of the cytological method is that synthesis of a single virus particle must be deduced from the multiplication of a virus population. The detection of intermediate stages in virus assembly, and the positions in the ceI1 where they appear are important elements in this process. So far, for one plant virus, TMV, and to a lesser degree for other viruses, a general outline of the multiplication cycle has been given. Intensive methods, such as UV-microspectrophotometric, fluorescent antibody techniques, and radioactive tracers have given accurate information within a small range. Phase and ordinary bright light microscopy have given less reliable information, but have told more about the infected cells as coordinated systems, and have more readily allowed comparisons between a numbers of virus-host combinations.