This full 'research' paper presents an overview of results of a systematic literature review of students' affective responses to active learning in undergraduate STEM courses. We considered 2,364 abstracts of conference papers and journal articles published since 1990, and 412 studies met our inclusion criteria. The studies span the STEM disciplines and report various types of active learning. Their research designs include primarily quantitative methods (especially instructor-designed surveys and course evaluations), and they find that students' affective responses are overwhelmingly positive. Few studies excelled on our quality score metric, and there few statistically significant differences by discipline (but biology studies and chemistry studies scored significantly higher in quality than electrical engineering studies). We include several possible directions for future work.