In mid 1980s, open education arrived in Korea. It was influenced by the educational reforms implemented in American primary schools. Currently, the Ministry of Education is appealing to teachers for their active involvement in educational reform by using open education methodology. Often teachers in Korea complain that they do not know what to do or how to change in order to practice the open education. It is time to review the state of open education in Korea and the United States. This paper contains the following segments: 0) Introduction, 1) Beginning of open education, 2) A brief history of open education in Korea, 3) The current status of open education in the United States, 4) A glance at open mathematics classroom in Korea, 5) Lessons from the review, and 6) Conclusion.