The authors define the basic elements of writing and writing systems: graphemic units (graphemes and allographs), graphetic units (letters and graphs) and typographical units (glyphs and characters). Starting with graphemes, they introduce and discuss different definitions of graphemes proposed in the pertinent literature and then tackle the question of the distribution of graphemes in a given writing system and elaborate on the concept of allography. Regarding graphetic units, the authors focus on the internal structure of letters and other graphs and introduce the concept of the ‘length hierarchy’ of letters, which leads to a discussion of larger graphemic categories, especially the graphemic syllable. Looking more deeply at the functional distribution of letters, they address the question of graphemic inventories and their development. Their discussion also includes the typographical key concepts of glyphs and characters. The chapter then focuses on the graphemic subinventory of punctuation, the form of punctuation marks, as well as their decoding and encoding functions. The final issue discussed is capitalization as the functional differentiation between uppercase and lowercase, including the development of different functions of uppercase letters in the history of the European writing systems.