In 1623, seven years after William Shakespeare died, two of his friends and fellow actors led an effort to publish a single volume containing 36 of the plays he had written, half of which had never been officially published before. Now known as the First Folio, that volume has become a lodestone of Shakespeare scholarship over the centuries, offering the most definitive versions of his work along with clues to his process and plenty of disputes about authorship and intention.In honor of its 400th anniversary, the British Library recently released a facsimile version of the First Folio. On this week’s episode, The Times’s critic at large Sarah Lyall talks with Adrian Edwards, head of the library’s Printed Heritage Collections, about Shakespeare’s work, the library’s holdings and the cultural significance of that original volume.