Society will not fully benefit from development and use of future discoveries and innovations if we do not provide full access and opportunity to engage in effective STEM education -- and we may lack the information, tools, and resources needed to address future challenges facing our planet. Commonly used methods of teaching undergraduate STEM education benefit only a relatively small percentage of learners, leading many to choose not to enroll in STEM courses or pursue STEM careers. This trend severely limits participation in the STEM careers that play a critical role in our nation's prosperity. High quality instruction, learning, and engagement in STEM should be a key priority for colleges and universities across the United States. Transforming Undergraduate STEM Education: Supporting Equitable and Effective Teaching calls on leaders of institutions and academic units, instructors, and other stakeholders to leverage their important roles to improve the landscape of undergraduate STEM education so that all students can thrive. As one step toward addressing inequities and transforming undergraduate STEM education, this report presents a set of Principles for Equitable and Effective Teaching. These Principles provide guidance for instruction that draw on decades of research on teaching, learning and equity. Transforming Undergraduate STEM Education provides guidance for improving teaching and related changes to the institutional context that are needed to support instructors and enable student-centered undergraduate STEM education.