In 2021, California committed to making transitional kindergarten (TK)—a school-based preschool program initially designed for older 4-year-olds—available for all 4-year-olds by 2025–26. As TK becomes universal, California will need to greatly expand the early learning workforce. This report and brief from the Learning Policy Institute provides estimates of how many TK teachers California will need; describes the potential supply pools that could meet this demand; outlines pathways into the profession; and offers recommendations to help stabilize, support, and expand the entire early childhood workforce.