"Essential Questions & Data Sources for Continuous Improvement of Undergraduate STEM Teaching and Learning" is intended to be a useful resource for the individuals and institutions who work together to help foster continuous improvement of undergraduate STEM education. Informed by the broad literature on post-secondary STEM education, this resource draws primarily from the Association of American Universities' experience in implementing the AAU Undergraduate STEM Education Initiative with our member campuses. It provides a set of questions that can be used at multiple levels within the university to assess progress along the set of key institutional elements identified in AAU's "Framework for Systemic Change in Undergraduate STEM Teaching and Learning" (ED613653). Questions are presented to examine the pedagogical, scaffolding, and cultural elements of the framework at each organizational level in the institution. Data sources and analytical tools available to answer these questions are profiled in a subsequent section. A final section provides guidance to address cross-cutting challenges to assessing improvement of undergraduate STEM teaching and learning.