The aim of this article is to present the content of instruction needed in designing a discussion class, in view of Canale and Swain's communicative competence and Toulmin's argument model. In a broad sense, discussion is regarded as an interactive communication dealing with some particular topic. Thus the content of discussion instruction should be based on the characteristics of communication as well as critical thinking. To improve communicative ability, the content of discussion instruction includes grammar and vocabulary related to the given subject in terms of linguistic competence, textual organization in terms of discourse competence, social roles, formality and styles in terms of sociolinguistic competence, and finally linguistic strategy in terms of strategic competence. To improve critical thinking ability, the content of discussion instruction includes the elements of argument like grounds, warrant, modality, claims, backing and possible rebuttals. This study concludes with a suggestion of a model discussion class. (Seoul National University)