No issue in Shakespeare studies is more important than determining what he wrote. For over two centuries scholars have discussed the evidence that Shakespeare worked with co-authors on several plays, and have used a variety of methods to differentiate their shares from his. In this wide-ranging study, Brian Vickers takes up and extends these discussions, presenting compelling evidence that Shakespeare wrote Titus Andronicus together with George Peele, Timon of Athens with Thomas Middleton, Pericles with George Wilkins, and Henry VIII and The Two Noble Kinsmen with John Fletcher. In Part One Vickers reviews the standard processes of co-authorship as they can be reconstructed from documents connected with the Elizabethan stage, and shows that every major, and most minor dramatists in the Elizabethan, Jacobean, and Caroline theatres collaborated in getting plays written and staged. This is combined with a survey of the types of methodology used since the early nineteenth century to identify co-authorship, and a critical evaluation of some 'stylometric' techniques. Part Two is devoted to detailed analyses of the five collaborative plays, discussing every significant case made for and against Shakespeare's co-authorship. Synthesising two centuries of discussion, Vickers reveals a solidly based scholarly tradition, building on and extending previous work, identifying the co-authors' contributions in increasing detail. The range and quantity of close verbal analysis brought together in Shakespeare, Co-Author present a compelling case to counter those 'conservators' of Shakespeare who maintain that he is the sole author of his plays.