Maurice Sendak, who died in 2012, left the bulk of his personal library of rare books to the Rosenbach of the Free Library of Philadelphia. The author-illustrator’s estate contested the will, and the case was recently settled. The Sendak estate ended up retaining 252 of the books – including two worth millions. But the Rosenbach received 643 books, rounding out existing collections and creating new strengths for Philadelphia’s small museum and library a few blocks from Rittenhouse Square. Rosenbach director Derick Dreher explains why some of the new acquisitions were so important to Sendak.