Recognizing that empirical research into classroom dialogue has been conducted for about 40 years, a review is reported of 225 studies published between 1972 and 2011. The studies were identified through systematic search of electronic databases and scrutiny of publication reference lists. They focus on classroom dialogue in primary and secondary classrooms, covering the full age range of compulsory schooling. The methods of data collection and analysis used in the studies are described and discussed, with changes and continuities over time highlighted. Study results are then summarized and integrated to present a succinct picture of what is currently known and where future research might profitably be directed. One key message is that much more is known about how classroom dialogue is organized than about whether certain modes of organization are more beneficial than others. Moreover, epistemological and methodological change may be required if the situation is to be remedied.