This chapter discusses the notion of orthographic principles, the associated theoretical issues and the relevance of these principles in the (diachronic) study of spelling. It provides an overview of the aspects of writing that should be taken into consideration when identifying general patterns or rules governing spelling practices within a specific historic orthographic system, such as the typological make-up of the writing system, levels and regularity of linguistic representation, and graphotactic constraints. The discussion focuses on alphabet-based spelling systems and delineates several general pathways for the conventionalization of spelling across various European vernacular spellings systems at different historical periods, making particular illustrative use of Cyrillic Lithuanian. In addition to foregrounding the importance of sound-oriented and meaning-oriented graphic mappings in shaping alphabet-based spelling systems, this chapter emphasizes the role of graphotactic constraints, which have been central in contributing to morphographization of some European spelling systems in the early modern and late modern periods.