Abstract This study examines complex, dynamic interactional sequences in which multilingual students co-construct improvisational humor when encountering miscommunication in an academic writing classroom at an U.S. university. Combining multimodal conversation analysis with ethnographic information, this study captures (a) the dynamic way that humor emerges among multilingual students and their instructor in classroom interactions and (b) the multiple activities besides humor construction that the students and their instructor engage in while the humorous and/or laughable sequences emerge. The analysis suggests that humor construction can be a powerful resource for enacting language learner agency (e.g., Larsen-Freeman, 2019 ) in adapting diverse linguistic and other multimodal elements in the classroom. Such analyses can project multilingual students as competent English users and demonstrate their interactional competence. Furthermore, this study illustrates the intricate ways that learner agency is constantly affected by diverse elements, including teacher instructional management, in the classroom.