This volume of New Directions for Evaluation focuses on evaluation of science, technology, engineering, and mathematics (STEM) programs, with special emphasis on evaluation of STEM education initiatives. STEM evaluation has always been important, given the issues facing public schools and the economic and social considerations of STEM fields. But because these fields today face a variety of concerns, this discussion of STEM evaluation is particularly timely. Evaluation advances may contribute to STEM fields by helping programs address the challenges they face. This volume presents multiple viewpoints and state-of-the-art examples and methodological approaches in the hope that its chapters will contribute to the understanding of STEM evaluation, STEM education, STEM education evaluation, and evaluation in general. Overall, this volume of New Directions for Evaluation may help not only to move the field to consider new methods and methodologies for engaging in evaluation but also to reconsider ideas of what it means to engage in scientific evaluation.