The purpose of this study was to design and develop an interactive digital textbook in middle school English for both the classroom and individualized (differentiated) learning. Most of digital textbooks developed so far have been mainly focused on the digitization of text like an e-book, but not sufficiently utilized the interactive features of computer. Therefore, in this study, we attempted to find a way to develop the digital textbook to support students' individualized learning as well as classroom learning by accommodating various needs of individual learners and English education. For this, we devised the design principles for the development of digital textbook based on the theoretical review, which consisted of two dimensions of activities (Representation of information and Expression of understanding) and three categories of cognitive aspects (Recognition, Strategy, and Affection). Then, we applied them to the development of the English digital textbook. In this paper, we introduced the examples of the design principles applied in it and some implications for the development of digital textbook.