Executive functioning (EF) is an important developing self-regulatory process that has implications for academic, social, and emotional outcomes. Most work in EF has focused on childhood, and less has examined the development of EF throughout adolescence and into emerging adulthood. The present study assessed longitudinal trajectories of EF from ages 10 to 21 in a diverse, international sample. 1093 adolescents (50.3% female) from eight locations in seven countries completed computerized EF tasks (Stroop, Tower of London [ToL], Working Memory [WM]) at ages 10, 14, 17, and 21. Latent growth curve models were estimated to understand the average performance at age 10 and the change in performance over time for each task. Meta-analytic techniques were used to assess the heterogeneity in estimates between study sites. On average, EF task performance improved across adolescence into young adulthood with substantial between-site heterogeneity. Additionally, significant individual differences in EF task performance at age 10 and change in EF task performance over time characterized the full sample. EF improves throughout adolescence into young adulthood, making it a potentially important time for intervention to improve self-regulation.