In Shakespearean scholarship, a bad quarto is a quarto-sized publication of one of Shakespeare’s plays that is considered spurious, that was pirated from a theatre without permission by someone in the audience writing it down as it was spoken. Or it would be written down later by an actor or group of actors, which, according to the theory, has been termed “memorial reconstruction”. In this way the quarto derives from performance, and since it lacks a direct link to the author’s original manuscript, it is a text that would be expected to contain corruptions, abridgments and paraphrasings. This is in contrast to a “good quarto”, which is considered to be a text that is authorized; one that may have been printed from the author’s manuscript, or a scribal copy or prompt copy based on the author’s manuscript. "Bad quartos" are considered to include the first quartos of Romeo and Juliet, Henry V, The Merry Wives of Windsor, and Hamlet.
The concept has expanded to include quartos of plays by other Elizabethan authors, including Peele’s The Battle of Alcazar, Greene’s Orlando Furioso, and the collaborative script, Sir Thomas More.
The bad quarto theory has been accepted, studied and expanded by many scholars, but there are scholars who do not accept it, and those, such as Eric Sams, who consider the entire theory to be without foundation. Jonathan Bate states that “late twentieth- and early twenty-first century scholars have begun to question the whole edifice.”
The concept of the “Bad Quarto” as a category of text was created by bibliographer Alfred W. Pollard in his book Shakespeare Folios and Quartos (1909). The idea came to him in his reading of the address by the editors, John Heminges and Henry Condell, that appears at the beginning of Shakespeare’s First Folio. This address is titled, “To the Great Variety of Readers.” In this address Heminges and Condell refer to “diuerse stolne, and surreptitious copies” of the plays. It had been thought that that reference was generally to quarto editions of the plays. Pollard, however, claims that Heminges and Condell meant to refer only to “bad” quartos, and Pollard lists as “bad” the first quartos of Romeo and Juliet (1597), Henry V (1600), The Merry Wives of Windsor (1602), Hamlet (1603), and Pericles (1609). Pollard points out that the texts contained “badness”, but also that there was badness in those who pirated the plays.