This book explores the nature and causes of misunderstandings in ELF interactions. It is based on a corpus of conversations between English speakers from south and east Asia that helps us investigate what causes misunderstandings, particularly the pronunciation, grammar, word choice, and discourse. The book also considers how such misunderstandings may be signalled and repaired. Finally, it discusses the implications for teaching English around the world and offers guidance to teachers in enabling their students to become highly intelligible.