Blindsight is the ability, still controversial if a vote is taken, of subjects with clinically blind field defects to detect, localize, and discriminate visual stimuli of which the subjects say they are completely unaware—the original definition—or of which they might be aware but not in the sense of experiencing a visual percept. These two conditions are known as blindsight Types I and II. This Bartlett lecture narrates the discovery of blindsight and its mounting opposition, and it evaluates the continuing and often perplexing debate about its standing as a visual cognitive phenomenon.