The purpose of this study was to explore the co-teaching experiences between native and non-native English teachers in the Korean elementary and secondary school context. Research data included classroom observations and teachers’ interviews collected over one school semester. A constant comparative data analysis method was employed to provide an in-depth description of the co-teachers’ teaching practice, the aspects of their interactions, and their professional development in a classroom setting. The findings of this study revealed that the co-teaching styles and role distributions in the co-teaching process were different depending on the non-native teachers’ English proficiency and their professional relationships. It also suggested that the successful implementation of collaborative team work was deeply related to the participating teachers’ willingness to cooperate and conceptions created by the dynamics of interaction between the two teachers in and outside of the classroom. Given the research result that both native and non-native teachers benefitted from their co-teaching experiences, some pedagogical implications on the improvement of co-teaching English in Korean classrooms are proposed.