〈特集〉現代東南アジアにおける宗教の越境現象―タイ，ミャンマーを中心に― This special issue focuses on religious boundary-crossing in contemporary Thailand and Myanmar. Thesetwo countries have long inspired scholars of frontier studies as well as religious studies of Southeast Asia.Recent developments in trans-border mobility between Thailand and Myanmar have also contributed togreater interest among scholars in Thai and Myanmar studies, for example in boundary-crossing religions.In this special issue, we use the term “boundary” in three dimensions: national boundary, ethnic boundary, and boundary of institutionalized religions.We start our discussion with an optimistic expectation of increased resistance from peripheries againstnation-states, state-sanctioned ethnic categories, and religions institutionalized by such states. However, discussions based on each field reveal more complex realities. In some cases, the Buddhism practiced bymulti-ethnic local populations has recently undergone categorization according to ethnicity due to the increasedmobility of religious leaders. Many charismatic monks are enthusiastically worshipped by marginalizedethnic minorities along the frontiers of nation-states. However, we find that they are by no meansantagonistic to existing state power. Missionary Buddhism is supposed to be a typical form of religiousboundary-crossing. Nevertheless, through this activity, the very concept of Buddhism is questioned whenmissionary monks are forced to observe their precepts in an environment without lay support.Essays in this special issue are reflections from our struggle to understand and explain the complexsituations faced by contemporary Southeast Asian religions. Needless to say, our conclusions are not definitiveanswers to these questions. Rather, we would like to invite readers to join the ongoing discussionon these challenging topics.