A folio is a large book in which printed sheets are folded in half only once, creating two double-sided leaves, or four pages. Folios were more expensive and far more prestigious than quartos. Seven years after Shakespeare's death, John Heminge and Henry Condell, his friends and colleagues in the King's Men, collected almost all of his plays in a folio edition. Shakespeare's friendly rival Ben Jonson had previously published his own writings, poems included, in a folio. The 1623 First Folio of Shakespeare, however, is the earliest folio consisting only of an author's plays.
The First Folio groups the plays for the first time into comedies, histories, and tragedies, and it includes the Droeshout portrait of Shakespeare, generally considered an authentic image because it was approved by those who knew him. More importantly, the First Folio preserved 18 of Shakespeare's plays that had never been printed before:
Researchers believe that 750 or fewer copies of the First Folio were printed; 233 survive today, of which 82 are in the Folger collection. Each one is slightly different, partly because proofing took place at the same time as printing. Being able to compare different copies side-by-side has greatly increased our understanding of the volume. A full digital version of one of the Folger's First Folios (no. 68) can be viewed in the Folger Shakespeare Library's digital image collection for downloading.