Despite astronomy's widespread inclusion in curricula prior to the twentieth century, educational research in astronomy is a relatively new endeavor. As the field of astronomy education research grows, many may find it useful to know what has been done so far. Starting with and expanding beyond the SABER database, a systematic review and classification of the K-12 and higher education literature was performed. Some of the research themes that emerged include: student beliefs and misconceptions; collaborative learning; the large
lecture classroom; and education in planetariums. Key studies in these areas are described and a bibliography is presented.