Book excerpt: The structure and content of a contemporary second language textbook are intended to encourage the initiative learner activity and create proper conditions for its manifestation in the curriculum. This premise unreservedly accepted by the teaching community proposes a flexible approach to second language acquisition encouraging individual self-learning experience. Textbook Theory and Invariant Approaches to Language Learning: Emerging Research and Opportunities is a critical scholarly publication that examines the structure and function of current second language learning curricula and classrooms. The book pursues three main objectives, which include (1) reconstruction of the general conceptual framework of textbook theory; (2) systematization of the invariant approach applications; and (3) production of a set of concepts, principles, rules, and regularities underlying the invariant-based text development. Featuring a wide range of topics such as learning patterns, proficiency, and communication, this book is ideal for education professionals, academicians, professionals, researchers, curriculum designers, and students.