This chapter is intended to offer assistance for the linguistic description of writing systems throughout the history of one or, especially, several languages and provide a comparative description of the different units of writing systems. The first section establishes the definitions of the concepts of grapheme, graph, allograph and suprasegmental grapheme. The application of these concepts to English and Romance languages is exemplified by three models and methods of diachronic and comparative description of writing systems: Romance scriptology, cultural history of European orthographies, and comparative graphematics of punctuation. The second section discusses biscriptality, the phenomenon of employing two or more writing systems for the same language, not rare in the history of languages from different families, and related to different aspects of society and language users. With examples mainly from Russian and other Slavic languages, biscriptality is shown to be present on several levels of written language, and various applications of biscriptality are characterized with the help of dichotomies such as synchronic vs. diachronic biscriptality, monocentric vs. pluricentric biscriptality, and societal vs. individual biscriptality.