It may take a decade or two before the extent of Shakespeare's collaboration passes from the graduate seminar to the undergraduate lecture, and finally to popular biography, by which time it will be one of those things about Shakespeare that we thought we knew all along. Right now, though, for those who teach the plays and write about his life, it hasn't been easy abandoning old habits of mind. I know that I am not alone in struggling to come to terms with how profoundly it alters one's sense of how Shakespeare wrote, especially toward the end of his career when he coauthored half of his last ten plays. For intermixed with five that he wrote alone,,,,, and, are (written with Thomas Middleton), (written with George Wilkins), and, the lost, and (all written with John Fletcher).