This article reviews published research on (i) classrooms as communities; (ii) classrooms as communities of learners; and (iii) classrooms as learning communities. It is based on a reading of about 100 texts. It aims to answer the question "What do we now know about the effects of operating classrooms as learning communities?". Despite the fact that this mode of operating classrooms is not the dominant one, and is correspondingly under-researched, there is good evidence that it brings significant benefits.