‘This Handbook offers a panoramic and generative synthesis of 25 years of scholarship, tracing Universal Design for Learning (UDL) from its early CAST origins to its current status as a global framework shaping instructional design, policy, and technological innovation. The editors craft a historically grounded narrative showing how UDL evolved alongside shifts in digital ecosystems, accessibility movements, and research in learning sciences. The text demonstrates how UDL has become a shared design language for educators, technologists, researchers, and architects committed to building environments structured for learner variability from the outset.