While the antique book market isn't what it once was, appraisal expert Allan Stypeck says rare, autographed and original editions, especially manuscripts, are still highly valued. Because books are usually passed down through relatives over the years, many of his clients have no idea what theirs could fetch at auction. "A woman recently called and said she had a book she thought might be worth something," Stypeck says. "It turned out it was a 13th-century illuminated [handwritten and illustrated] manuscript from a monastery in Paris that was worth a minimum of $30,000." But because book appraising depends on a multitude of factors (edition, condition and rarity) Stypeck doesn't recommend trying to figure out your books' value on your own. The Antiquarian Booksellers' Association of America (abaa.org) has a directory of rare booksellers who can get you on the right track.