Why do questions about idioms often leave us "tongue-tied" in our classrooms? This book takes a look at learning and teaching idioms from two perspectives. First is a survey of recent work on learning and teaching idioms from diverse perspectives in the linguistics and educational research literature. The survey includes definitions of idioms from theoretical and pedagogical literature, focusing in particular on cognitive, cross-linguistic, and social constructionist research. Second is a summary and critique of idiom textbooks and classroom practices from around the world.