As a leading figure in the Wittgensteinian school, Karin M. Fierke has established the “Language Game” Constructivism by introducing Wittgenstein’s idea of language game into the analysis of international relations, on the basis of which she develops her unique constructivist theory that is characterized by an emphasis on rule, rationality, and acting as if. Fierke also reveals the importance of daily language in constructive games from the perspectives of naming, analogy, metaphor, trauma, and besting. In her engagement with the debate over the enlargement of NATO, Fierke criticizes the Neorealist and Neoliberalist explanations, and contributes to the Constructivist thesis through an insightful analysis from the perspective of language game.