A post-pandemic world has sparked a drive to reassess meanings of and ways to build connections and relationships in our lives. Specifically in education, teacher collaboration has been encouraged to combat such a task (UNESCO, 2020). Although communities of practice (CoP) for such collective learning itself is not a new phenomenon, more innovative challenges require Landscape of Practice (LoP) where teachers learn through boundary crossing and participation in CoP (Wenger-Trayner, et. al., 2015). Interdisciplinary teacher collaboration (ITC) where an English teacher works with a content teacher towards a shared goal is one way to actualize this LoP. Nevertheless, when to or why we cross such boundaries are not well documented (Lu, 2020). Therefore, this ongoing case study aims to explore ITC’s impact on teachers’ decision making in designing, implementing, and evaluating an elective business-content ESP course for Spring 2022 at a private university in Japan. This study will collect and examine a variety of data related to ITC from email to casual oral chats during December 2021 to July 2022. The findings will show how and when ITC influences teacher’s decision making in designing an ESP course to enhance students’ learning in the post-pandemic world.