Research on charter schools tends to focus on direct and immediate effects on student outcomes. However, there may be unintended indirect effects on, for example, the teacher labor market. Charter schools tend to hire younger, less experienced teachers with fewer traditional teaching credentials, which may reduce the equilibrium quantity of teachers who have traditional credentials and seek to make teaching a career. We test whether charter entry reduces the supply of university-trained teacher education majors, exploiting cross-district variation in the timing of charter school entry in districts containing college teacher preparation programs. Applying a matched difference-indifference model, we find evidence that, for example, a 10 percent increase in charter market share decreases the supply of traditionally prepared teachers by 13.5 to 15.2 percent on average. This effect is concentrated in metropolitan areas and for elementary, special education, and math education degrees. [For the corresponding brief, "How Do Charter Schools Affect the Supply of Teachers from University-Based Education Programs? Policy Brief," see ED624454.]