For more than a decade, academics and education policy experts have raised concerns about a widespread shortage of teachers in the United States. The first wave of warnings came in response to the drastic cuts in state and local spending on education following the Great Recession. In this report, the authors use data from a wide range of sources to document the size and scope of the teacher shortage. The data show that the teacher shortage is both widespread and acute across several dimensions, from subject matter specialties to school poverty status. The authors also review data that point to the two most important drivers of the shortage: (1) the declining compensation in the teaching profession relative to other occupations that employ college graduates; and (2) and the increasingly stressful work environment teachers face, a long-standing reality that has been greatly exacerbated by COVID-19. The key finding is that the current shortage is generally "not" the result of an insufficient number of potentially qualified teachers. The shortage is, instead, a shortfall in the number of qualified teachers "willing to work at current wages and under current working conditions." The combination of substandard teacher compensation and highly stressful working conditions has, in recent decades, made teaching a much less attractive profession than alternatives available to workers with college degrees.