In the context of constantly increasing linguistic diversity in many parts of the world, opportunities and challenges arise for the acquisition of literacy skills. The successful development of literacy skills becomes a crucial prerequisite for educational attainment determining future career prospects of migrant students. Multilingual settings reveal the diversification of languages and scripts prompted in the context of migration. This monograph explores the phenomenon of biscriptuality and aims to provide an approach for investigating the development of biliteracy in the context of divergent scripts. This interdisciplinary mixed-methods study bridges intercultural education science, education research and applied linguistics for gaining a complex view on the role of biscriptuality in students' biliteracy. It considers the extent of students' biscriptual skills, specifies language dimensions in which the influence on biliteracy may occur, and differentiates between the effects of biscriptuality on the development of writing skills in two different genres, narrative and expository.