This chapter demonstrates how first-year international students enrolled in a semester-long ESL writing course in a mid-sized US university benefitted from a project-driven syllabus focused on environmental sustainability. Projects included 1) collaborating with domestic peers enrolled in an environmental geology course for non-majors on Do Now U, a national science blogging project; 2) presenting academic posters on environmental problems on campus Sustainability Day; and 3) producing public service announcement videos on green practices for campus social media. International students reported increased confidence in their writing skills, such as selecting appropriate sources for academic research, preparing summaries, writing counterarguments, and improving academic vocabulary. PBL exposed international students to elements of undergraduate research by requiring them to interview subject-area experts and to speak extemporaneously about their research to members of the campus community. Furthermore, domestic students reported that working with international students on Do Now U was a new and valuable intercultural experience for them. In addition to offering multiple opportunities to participate in academic discourse throughout the semester, PBL positioned international students to matter and to belong in the campus community.