This work highlights the similarity in the fundamental conception about language that can and should be shared by theoretical linguists, language acquisition specialists and language professionals – linguistic competence is essentially a mental grammar, a linguistic system internalized by users according to the primary linguistic data accessible to learners. Recognizing this would bring the focus of language learning processes to learners themselves rather than instructors and draw attention to the importance of input in the target language. Accordingly, curricula can be more effectively designed and better practices adopted in language classrooms. Specifically, I will show how formal generative linguistic studies, as well as relevant second language acquisition research, can help us better understand and also provide guidance and support for the “best practices” in foreign language education currently advocated in the US. Some concrete examples will be provided to illustrate applications of the theoretical studies and implementations of the best practices.