I, as a teacher researcher, would like to argue that the exploration of language teacher cognition is important for all language teachers to develop their professional teaching knowledge and skills. This book explores that Japanese non-native English-speaking EFL (English as a foreign language) teachers in secondary education, which is called JEFL teachers in this book, work in a different educational context from language teachers in other countries. Moreover, this study is also the exploration of my own teacher kokoro(こころ, 心), which is a Japanese term probably equivalent to teacher cognition in the Japanese context. Based on the present study, I hope I will upgrade the term 'language teacher cognition' to 'language teacher kokoro' in order to further see such complex aspects of the nature of language teacher cognition and to start language teacher kokoro research.