This work explores the development and implementation of Communities of Practice (CoP) within “Big Science” Organizations. A CoP is a group of professionals who share a common interest, profession, or passion and actively engage in collaborative learning and knowledge sharing (Wenger, 1998). In the context of “big science” (e.g., large-scale observatories), a CoP plays a crucial role in fostering collaboration, enhancing knowledge exchange, and driving innovation across multiple facilities, especially in the domain of cyberinfrastructure (CI). Based on 23 interviews conducted with directors, project staff, technical staff, and scientists across various “big science” organizations funded by the National Science Foundation (NSF) called Major Facilities (MFs), we used the grounded theory approach (Corbin & Strauss, 1990) as our method to analyze the data. We found eight themes that describe what MFs do to build a CoP: identifying common interests and challenges, promoting knowledge sharing, organizing guest sessions, providing networking opportunities, creating an inclusive environment, facilitating collaborative projects, and exploring new partnerships.