With 23 campuses serving nearly 500,000 students, the California State University (CSU) is the largest and most diverse university system in the country. Annually, 3,500 service-learning (SL) courses are offered to more than 67,000 students, 17% of whom are science, technology, engineering, and mathematics (STEM) majors. However, there is little data on the landscape of these courses and the extent to which they are implemented with fidelity and quality across campuses. This article will summarize the first system-wide, multi-year research study assessing SL in STEM courses and address key gaps in the literature. Specifically, the article will explore how SL is implemented in STEM disciplines across a sample of CSU institutions, common underlying elements in course implementation, and the overall quality of those SL elements within courses. In addressing these questions, this article will also discuss the development of study instruments and the resulting codification of essential SL elements.