A community of practice (CoP) consists of individuals who ally with one another to pursue topics or goals of common interest. The goal of CoP membership is to deepen one's knowledge and gain additional expertise from the community's more experienced members. In English language teaching, CoPs have typically been implemented with classroom learners. Alternatively, they may also be implemented with teachers for the purpose of ongoing professional development. This entry concerns the latter case, initiated in the five countries in the Lower Mekong region of Southeast Asia as part of a larger US government project. The goal of this project, the Professional Communication Skills for Leaders (PCSL) CoP, was to create transnational alliances among teachers in the region and better prepare them to teach English for professional purposes to local experts in environment, health, infrastructure, energy development, and agriculture. The entry provides information on the implementation of the project and how it is being sustained.