His Dark Materials
Pullman, Philip
Paperback
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Awards:
2002 Whitbread Book of the Year Prize
3rd Place in 2003 BBC Big Read Poll
1995 Northern Lights (The Golden Compass) Carnegie Medal

His Dark Materials is a fantasy trilogy that follows the adventures of Lyra Belacqua and Will Parry, as they discover what is happening to all the children travel to alternate universes and test themselves. It is comprised of three separate novels: The Golden Compass (1995 - Published as The Northern Lights everywhere but North America), The Subtle Knife (1997), and The Amber Spyglass (2000).  The Title of the series, His Dark Materials, is said to have come from 17th century poet John Milton's Paradise Lost, Book 2:

Into this wilde Abyss,
The Womb of nature and perhaps her Grave,
Of neither Sea, nor Shore, nor Air, nor Fire,
But all these in their pregnant causes mixt,
Unless th'Almighty Maker them ordain
His dark materials to create more Worlds.
Into this wilde Abyss the warie fiend
Stood on the brink of Hell and look'd a while,
Pondering his Voyage; for no narrow frith
He had to cross.
-- Book 2, lines 910-920

I suggest one picks up the entire triology at once, because once you finish the first book you won't want to wait to get started on the second, and the third.  Pullman has also been working on some companion books to go with the trilogy.  Lyra's Oxford, Once Upon a Time in the North, a book about Will, and The Book of Dust.  The book about Will and The Book of Dust have yet to be released.  You can find out more about Philip Pullman, his novels, and his future works at his website, here, where he writes, "As a passionate believer in the democracy of reading, I don't think it's the task of the author of a book to tell the reader what it means." And be sure to check out this interview with Pullman over at the TimesOnline.

Summaries:

The Golden Compass

In a landmark epic of fantasy and storytelling, Philip Pullman invites readers into a world as convincing and thoroughly realized as Narnia, Earthsea, or Redwall. Here lives an orphaned ward named Lyra Belacqua, whose carefree life among the scholars at Oxford's Jordan College is shattered by the arrival of two powerful visitors. First, her fearsome uncle, Lord Asriel, appears with evidence of mystery and danger in the far North, including photographs of a mysterious celestial phenomenon called Dust and the dim outline of a city suspended in the Aurora Borealis that he suspects is part of an alternate universe. He leaves Lyra in the care of Mrs. Coulter, an enigmatic scholar and explorer who offers to give Lyra the attention her uncle has long refused her. In this multilayered narrative, however, nothing is as it seems. Lyra sets out for the top of the world in search of her kidnapped playmate, Roger, bearing a rare truth-telling instrument, the compass of the title. All around her children are disappearingvictims of so-called "Gobblers"and being used as subjects in terrible experiments that separate humans from their daemons, creatures that reflect each person's inner being. And somehow, both Lord Asriel and Mrs. Coulter are involved.

The Subtle Knife

The highly anticipated second installment of Philip Pullman's epic fantasy trilogy. Lyra and Will, her newfound friend, tumble separately into the strange tropical otherworld of Cittagazze, "the city of magpies," where adults are curiously absent and children run wild. Here their lives become inextricably entwined when Lyra's alethiometer gives her a simple command: find Will's father. Their search is plagued with obstacles--some familiar and some horribly new and unfathomable--but it eventually brings them closer to Will's father and to the Subtle Knife, a deadly, magical, ancient tool that cuts windows between worlds. Through it all, Will and Lyra find themselves hurtling toward the center of a fierce battle against a force so awesome that leagues of mortals, witches, beasts, and spirits from every world are uniting in fear and anger against it. This breathtaking sequel will leave readers eager for the third and final volume of His Dark Materials.

The Amber Spyglass

Along with the return of Lyra, Will, Mrs. Coulter, Lord Asriel, Dr. Mary Malone, and Iorek Byrnison the armored bear, come a host of new characters: the Mulefa, mysterious wheeled creatures with the power to see Dust; Gallivespian Lord Roke, a hand-high spymaster to Lord Asriel; and Metatron, a fierce and mighty angel. So, too, come startling revelations: the painful price Lyra must pay to walk through the land of the dead, the haunting power of Dr. Malone's amber spyglass, and the names of who will live--and who will die--for love. And all the while, war rages with the Kingdom of Heaven, a brutal battle that--in its shocking outcome--will uncover the secret of Dust. Philip Pullman deftly brings the cliff-hangers and mysteries of His Dark Materials to an earthshattering conclusion--and confirms his fantasy trilogy as an undoubted and enduring classic.