This introductory chapter makes the case for assessing the quality of English-Medium Instruction (EMI) faculty professional development (PD) by connecting program design, implementation, and impact, as a pathway for overcoming the pessimism that predominates in much EMI research. To do so, we begin by critiquing the focus in prevailing research on EMI policy, perceptions, and proficiency, which excels at documenting challenges while offering limited guidance for improvement. In particular, such research notably neglects pedagogy—the most impactful site for meaningful intervention. Drawing on our experience developing EMI faculty support in Taiwan, along with a critical synthesis of recent reviews of EMI faculty development initiatives, we advance a change-based vision of EMI faculty PD that emphasizes creating conditions for sustainable improvements in instructional practices with demonstrable impacts on student learning. Five research imperatives are articulated to guide this paradigmatic shift: (1) documentation of context-specific program design, (2) description of the pedagogical logic underlying program implementation, (3) rigorous assessment of program impact, (4) reporting of systematic institutional support for faculty development and professionalization, and (5) critical reflection from faculty developers. The chapter concludes with an overview of the nine subsequent chapters from diverse global contexts that respond to these imperatives and exemplify how transparently connecting PD design decisions, implementation strategies, and impact evidence can contribute to reframing EMI from a well-documented challenge to a ripe opportunity for educational transformation.