Abstract: "Broadband internet has become a critical component of U.S. infrastructure, but policymakers are increasingly concerned that the widespread adoption of this technology has adversely affected adolescent mental health. To test this hypothesis, we use 2009–2019 National and State Youth Risk Behavior Survey data and leverage the nationwide rollout of broadband internet. First, we show that adolescents in states with greater broadband internet access reported spending more time online. Next, we find that a one-standard-deviation increase in broadband internet access was associated with a 9.3–16.5-percent increase in adolescent suicide ideation. While we document increases in suicide ideation for both girls and boys, the results are most pronounced for adolescent girls. Exploring potential mechanisms, we show that greater broadband internet access was associated with increases in cyberbullying and body dissatisfaction among adolescent girls and a reduction in the likelihood that adolescent boys reported getting an adequate amount of sleep."