The placement of English language learners (ELLs) in mainstream classrooms raises important questions about the preparation of mainstream teachers to work with ELLs. Grounded by the conviction that well-prepared teachers can make a difference in student learning, and informed by current views on teacher learning and by teacher preparation research, this article conceptualizes ELL teacher expertise as enhanced expertise. It describes this expertise along 3 primary dimensions, along with examples of practices and implications for teacher preparation. The three dimensions are: (a) understanding ELLs from a bilingual and bicultural perspective; (b) understanding how language and culture shape school experiences and inform pedagogy for bilingual learners; and (c) ability to mediate a range of contextual factors in the schools and classrooms where they teach. (Contains 1 figure.)