Qualified science, technology, engineering, and mathematics (STEM) teachers are critical in the provision of high-quality STEM education for all students. Through descriptive and regression analysis, we document how demographic characteristics, qualifications, and turnover rates of a nationally representative sample of public school STEM teachers have changed from 1988 to 2012. Over this time period, STEM teachers are more likely to be female, attend selective colleges, have graduate degrees, and have STEM qualifications. Although STEM teachers are no more likely to turn over than other teachers, this masks differential rates between high- and low-poverty schools. Moreover, our results highlight the importance of recruiting qualified STEM teachers to work in high-poverty schools and providing supports to help them thrive and remain in the classroom.