De imitatione Christi (“The imitation of Christ”) is possibly the most widely read Christian devotional work after the Bible. Composed by Thomas à Kempis in the first quarter of the 15th century, the book was immediately popular and was printed in some 745 separate editions before 1650. The Sion College Library collection, now held here at Lambeth, includes a copy of the 1640 edition previously owned by James Boswell (1740-1795), biographer of the essayist and man of letters, Dr Samuel Johnson. The ownership inscription on the book’s flyleaf reads, “James Boswell. Edinburgh 1781”.De imitatione Christi was a favourite of Boswell’s and he refers to it in his Life of Johnson; several of those passages have been written in manuscript at the beginning of the Sion copy: “Thomas à Kempis must be a good book [says Boswell], as the world has opened its arms to receive it. It is said to have been printed in one language or others, as many times as there have been months since it first came out.” Johnson himself was apparently in the habit of speaking on the subject of the various editions. One Monday in May 1784, he and Boswell were dining together when Boswell raised the question: “When I mentioned that I had seen in the King’s Library sixty-three editions of my favourite Thomas à Kempis, amongst which it was in eight languages, Latin, German, French, Italian, Spanish, English, Arabic, and Armenian, he said he thought it unnecessary to collect many editions, which were all the same, except as to paper and print; he would have the original, and all the editions which had any variation in the text.” If one thing can be said about the Sion College copy, Boswell’s own, it is certainly not the same as all the rest.