Chapter 7 indicates some of the possible ways in which those working in historical orthography can recognise patterns in how writing systems function. The first half of the chapter in particular seeks to illuminate some of the formal aspects of writing that more directly inform principles in orthography. In alphabetic writing systems, the set of rules, conventions, regularities, patterns or preferences that govern spelling practices and/or their interpretation can be divided into two individual groups: phonemic and morphological. The chapter also focuses in great detail on the relationship between orthography and sounds, together with some of the complexities underlying the interpretation of phonemes as a result of diachronic developments. The complexities inherent in analysing historical writing systems entails the issue of deciphering lost or enigmatic scripts, intended as one of the end results of the challenges related to interpreting historical writing. In most cases, I argue, the task is complicated by the paucity of evidence, its state of preservation and its typology. This topic constitutes the second part of the chapter.