In 2000, federally funded public adult education programs provided basic skills training and English language instruction to over 2.6 million students, or about 1.5% of the U.S. adult population. By 2021, enrollment had plummeted to under 900,000, or less than 0.4% of adults. What explains these declines? This policy brief describes the evolution of federally supported U.S. adult education over the past 25 years as it relates to demographic shifts and trends in costs, providers, and federal accountability policies. We organize our brief around five findings drawn from our analysis of federal reporting data and conclude with recommendations for policy and research. Our brief highlights the increasing importance of immigrants to this sector, rising costs, and missed opportunities for research due to inadequate data systems.