The third folio of Shakespeare's works was printed in 1663, and a second issue appeared in 1664 adding Pericles and six other plays. These six others are now considered apocryphal, though they had all been published previously in quartos with Shakespeare's initials or name on them. The supplement containing these seven plays was published by Philips Chetwind, but little is known of his intentions or sources. Pericles was popular on stage (though Jonson thought it a 'mouldy tale') and had already been published by both Blunt and Jaggard, printers of the first folio, so it seems not to have been omitted from the first folio because of issues around printing rights. It may have been that the editors and printers knew that Shakespeare only collaborated in writing it. If they excluded plays on this basis, this rationale might also have applied to The Two Noble Kinsman and Sir Thomas More (as David Scott Kastan has argued). This may also explain why Timon of Athens, generally believed to be co-authored with Thomas Middleton, seems to have been a late addition to the first folio while much recent scholarship has focused on Shakespeare as a collaborator, the first folio presents him as a playwright working alone. Henry VIII, though, now considered by most to be written collaboratively between Shakespeare and Fletcher, is listed with the Histories with no apparent anxieties about Shakespeare's co-author role. Debate continues.
Pericles (added to the third folio in 1663), is sometimes seen as difficult to place in a genre, moving between 'tragicomedy' and 'romance', and in this it has been dubbed a 'problem play' alongside Measure for Measure, All's Well that Ends Well and Troilus and Cressida. The Winter's Tale and The Tempest sometimes fall into this category too, though they are arguably more easily categorized as romances or tragicomedies.
The third folio is a rarer book than the second or fourth, perhaps because the Great Fire of London destroyed booksellers' copies in 1666.