The aim of this study is to illustrate English textbook writers' opinions about difficulties in writing teachers' guides. Five university professors and three secondary school teachers were invited for a semi-structured interview. They were writers of the English textbooks certified by the Ministry of Education in Korea. They mentioned that they had difficulties meeting the needs of experienced and novice teachers, providing extra tasks for different classroom situations, writing test items for summative evaluation, suggesting ideas for performance assessment, presenting rubrics and explanations in English for teachers' TEE (Teaching English in English) classroom management, and handling cross-cultural issues and information between Korean and English speaking countries. Based on the comments, this study proposes that for novice teachers, clear objectives for each unit should be provided, and for experienced teachers, many test items should be included in teachers’ guides. More studies should be carried out with regard to teachers' guide design, and greater emphasis should be placed on workshops for the development of practical and user-friendly teachers' guides.