The Association of Southeast Asian Nations (ASEAN) comprises 10 countries of Southeast Asia, namely Brunei, Myanmar, Cambodia, Indonesia, Laos, Malaysia, the Philippines, Thailand, Singapore, and Vietnam. It is a region of great linguistic diversity, with more than 1000 languages being spoken across the 10 nations. The language policies of the ASEAN nations promote the respective national languages and English as languages of education. This chapter provides a brief history of English in ASEAN in order to contextualize the current important roles of English as the lingua franca (ELF) of ASEAN. It describes the multilingual context of ASEAN and the developing role of English as an ASEAN lingua franca. The chapter considers the presence of distinctive linguistic and sociocultural features of ASEAN English. In any discussion of the linguistic and sociocultural features of ASEAN ELF, it is important to point out at the outset that ASEAN ELF is not a stable single variety of English.