The history of UDL is the history of a single idea gaining depth: that variability is the rule, and that good design anticipates it. What began as a curb cut became a technology lab, then a neuroscience-informed framework, then federal law, and finally a global, multilingual movement now grappling with equity, identity, and artificial intelligence. Four decades on, UDL’s founding question remains its sharpest tool — not “What is wrong with this learner?” but “What is wrong with this design, and how do we fix it for everyone?”