ASEAN declared English as its working language in November 2007. As a result, the language's significance and popularity have increased significantly in the region during subsequent years, to the point where it threatens to encroach on territory frequently allocated for national languages. This is particularly visible in public spaces, where it is so prevalent that it frequently goes unnoticed. This chapter will highlight the rapidly developing body of research on Southeast Asia's linguistic landscapes (LLs), with a particular emphasis on the use of English in the LLs of ASEAN's ten member countries and Timor-Leste. As we discovered, Southeast Asia is home to some of the world's most diverse ethnic groups, cultures, languages, histories, economies, and religions. English's pervasiveness is highlighted throughout, symbolically and as a lingua franca.