The most common definition of literacy is the ability to read and write. However, for teachers working with multilingual learners, the development of literacy skills is much more complex than this simple definition would suggest. Notions of literacy in the 21st century have evolved in response to a number of societal changes, such as globalization, large-scale human migration, and advances in digital technologies. This chapter considers how these societal changes have influenced conceptions and practices of literacy. It provides a brief overview of some important theoretical considerations that inform understandings of literacy development for multilingual learners, including critical literacy, multiliteracies, multimodal literacy, and translanguaging, and explores current conceptions of literacy to help second and foreign language (SFL) teachers better understand how to meet the literacy needs of multilingual learners in the 21st century, offering practical suggestions for teaching from a multiliteracies perspective.