The following books are either available or are scheduled to be released. I've included every kind of edition that has been published, even if they are now out of print.
San Francisco: Chronicle Books, 2015.
Cowritten with Elena Dunkle.
Companion volume to Hope and Other Luxuries.
Available in ebook (NOOK or Kindle edition), hardcover, paperback, and audio.
San Francisco: Chronicle Books, 2015.
Companion volume to Elena Vanishing.
Available in ebook (NOOK or Kindle edition), hardcover, and audio.
New York: Holt, 2010.
146 pages (hardcover).
New York: Square Fish, 2011.
176 pages (paperback).
Available in ebook (NOOK or Kindle edition), hardcover, paperback (used), and audio.
New York: Atheneum, 2009.
Sequel to The Sky Inside.
225 pages.
Available in ebook (NOOK or Kindle edition) and hardcover.
Available in the UK: paperback (used).
Available in Australia: paperback (used).
New York: Atheneum, 2008.
Prequel to The The Walls Have Eyes.
229 pages.
Available in ebook (NOOK or Kindle edition), hardcover, and audio.
Available in the UK: paperback (used).
Available in Australia: paperback (used).
New York: Henry Holt, 2005.
229 pages
(hardcover).
New York: Square Fish, 2011.
256 pages (paperback).
Available in ebook (NOOK or Kindle edition), hardcover (used), library binding, and paperback (used).
Available in Danish: hardcover (used).
New York: Henry Holt, 2005.
Book Three of The Hollow Kingdom Trilogy.
231 pages.
Available in ebook (NOOK or Kindle edition), hardcover (used), and paperback.
Available in Danish: hardcover and audio (used).
New York: Henry Holt, 2004.
Book Two of The Hollow Kingdom Trilogy.
216 pages.
Available in ebook (NOOK or Kindle edition), hardcover (used), paperback, large print, and audio.
Available in Danish: hardcover, paperback, and audio (used).
New York: Henry Holt, 2003.
Book One of The Hollow Kingdom Trilogy.
230 pages.
Available in ebook (NOOK or Kindle edition), hardcover (used), paperback, large print, and audio.
Available in Danish: hardcover, paperback, and audio (used).