Up-to-date FAQ page about the book (from The Leaky Cauldron)

Brief synopsis of the book (from the Scholastic catalog)
SPOILER WARNING: This synopsis is printed in white on a white background. If you want to read it, highlight it with your mouse and it will appear as if by magic...

Additional notes

• This is the fifth book of the novel series, the seventh Harry Potter book released (counting the two "school books")
• There are plenty of rumors and guesses out there about the contents of this book. Don't believe most of what you hear. There are a few details which JKR herself has revealed, and these are listed below. Pretty much anything else you hear is NOT true. 
• There is also a book cover image that has been circulated as the cover of The Order of the Phoenix. The cover image is from a contest held by HPGalleries about a year ago. This is simply a fan drawing, it isn't real. 
• Book five, also known as OP or OoP, will be released on June 21, 2003, according to Bloomsbury. I'll leave the following notes here just for interest sake:
• As of this writing (September 2, 2002), Rowling has not turned a finished manuscript in to her editor at Bloomsbury. According to sources there, it will be a minimum of five months from when she does finish the book to when it can be released. That means that if she would finish the book tomorrow, it would still not come out until February or March. Therfore there is no way that OP will be released any earlier than early spring 2003, no matter what. 
• September 19, 2002: Rowling states that the book has a beginning, a middle, and an end, and it's readable all the way through, but that she's tweaking it. The same day, she announces that she is pregnant with her second child. Also that day, it is reported that she has overwhelmingly won the copyright infringement case brought against her by Nancy Stauffer. After many, many months of no interviews and no news about book five, September 19 feels to fans like Christmas came early.
• Notes about the covers, from CBBC Newsround:
• "The contents of the book are so secret that even the artist, illustrator Jason Cockcroft, wasn't allowed to read it before drawing the cover. Instead J K Rowling and her editor at Bloomsbury, Emma Matthewson, came up with the idea and then told the artist the kind of image they wanted them to create. The adult cover, designed by Bloomsbury's Design director William Webb, is from a photograph by Michael Wildsmith and again shows a phoenix." 
• Mary GrandPre once again did the illustrations for the book. She was given the book to read in advance, a necessity since she drew chapter art as well as the cover.

 

• chapter-by-chapter synopsis
• day by day calendar of events in the book
• differences between the British and American versions

• This is the title that JKR gave for the fifth book in the series. She revealed this during the taping of the Today Show and verified it in an interview with Newsround (NR2)
• This book will be longer than GF, at 220,000 words. 
• Many fans assume that the title refers to a goups who will band together to fight Voldemort, possibly the "Old Crowd" Dumbledore sent Sirius to call together at the end of Goblet of Fire. 
• The phoenix in this title is possibly a reference to Fawkes, Dumbledore's pet phoenix, whose tail feathers are imbedded in the wands of both Harry and Voldemort. Fawkes seems to be playing a more and more important role in the mythos; perhaps this ancient bird is really connected directly to Godric Gryffindor himself...
• Harry will be in his fifth year at Hogwarts in this book, the events of which will presumably take place between July 31, 1995 and the end of June, 1996. 
• Interesting things to watch out for, if the usual progression of school life continues:
• At least one of Harry's classmates will be made a Prefect, assuming that there is always a fifth year prefect (the year Percy was given that honor).
• Now that Oliver Wood has left school, the Gryffindor Quidditch team will need some new players. Who will become the new Keeper? Who will step in as team captain? 
• Harry and his classmates will be taking their first set of tests, their OWLs.

What's going to happen in book 5? Here's a nice list of quotes by JKR herself which give you some idea. The list has been circulating in various fan groups online; I'm not sure who to give credit to. If you know, please let me know: 
 

"In book 5, we go into a whole new area, physically, an area you've never seen before, a magical world" (1) 

"What's very important for me is when Dumbledore says that you have to choose between what is right and what is easy. This is the setup for the next three books. All of them are going to have to choose, because what is easy is often not right." (1) 

 "You'll be seeing Mrs. [Arabella] Figg in book five, and you'll find out all about her." (2) 

Harry will see him [the real 'Mad-Eye' Moody] in book five (2) but he won't want to be the Defense Against the Dark Arts teacher after spending months in that trunk (7)

Why do some wizards/witches become ghosts and others don't? "You will find out much more about that in book five." (3) 

There will be a female Defense Against The Dark Arts teacher. (3, 7) 

"You see Lupin in Book Five. Yes you see a lot of old characters in Book Five." (4) 

Book five will be scary. Harry finds out a lot of things he hasn't stumbled across so far. (4) 

"The Dursleys are in the next book, and there's stuff coming with them that people might not expect." (5) 

"Ginny Weasley [little sister to Harry's best friend, Ron] will play more of a role in Book Five." (5) 

"In book five [Harry] has to examine exactly what death means, in even closer ways." (6) 

"You may see a little more of Mundungus and there's a new sorting hat song." (7)

"Yes, it is looking (like it will be as long as book 4) - it's already passed Azkaban, so I think yes, we are looking at Goblet of Fire length." (7)

Brief synopsis of the book (SPOILER ALERT: highlight to view)

"I say to you all, once again – in the light of Lord Voldemort’s return, we are only as strong as we are united, as weak as we are divided. Lord Voldemort’s gift for spreading discord and enmity is very great. We can fight it only by showing an equally strong bond of friendship and trust.” So spoke Albus Dumbledore at the end of Harry Potter’s fourth year at Hogwarts. But as Harry enters his fifth year at wizard school, it seems those bonds have never been more sorely tested. Lord Voldemort’s rise has opened a rift in the wizarding world between those who believe the truth about his return, and those who prefer to believe it’s all madness and lies – just more trouble from Harry Potter. Add this to a host of other worries for Harry…  A Defense Against the Dark Arts teacher with a personality like poisoned honey  A venomous, disgruntled house-elf  Ron as keeper of the Gryffindor Quidditch team  And of course, what every student dreads: end-of-term Ordinary Wizarding Level exams …and you’d know what Harry faces during the day. But at night it’s even worse, because then he dreams of a single door in a silent corridor. And this door is somehow more terrifying than every other nightmare combined.  In the richest installment yet of J.K. Rowling’s seven-part story, Harry Potter confronts the unreliability of the very government of the magical world, and the impotence of the authorities at Hogwarts.  Despite this (or perhaps because of it) Harry finds depth and strength in his friends, beyond what even he knew; boundless loyalty, and unbearable sacrifice.  Though thick runs the plot (as well as the spine), readers will race through these pages, and leave Hogwarts, like Harry, wishing only for the next train back. The opening lines of the book... The hottest day of the summer so far was drawing to a close and a drowsy silence lay over the large, square houses of Privet Drive. ... The only person left outside was a teenage boy who was lying flat on his back...[fades out]