Harry Potter and the Order of the Phoenix, which opens in cinemas in July, sees Harry's school friends taking a more central role in the battle against the evil Lord Voldemort.
Wands at the ready: Harry leads his Dumbledore's Army cohorts
Calling itself Dumbledore's Army, the group meets in secret to learn how to battle the Dark Arts.
Actors Bonnie Wright, 16, (Ginny Weasley), Matthew Lewis, 17, (Neville Longbottom), Katie Leung, 19, (Cho Chang) and newcomer Evanna Lynch, 15, (Luna Lovegood) are all members of the Army.
They talk to BBC News about being fans of the schoolboy wizard, and what it is like being part of the Potter phenomenon.
WERE YOU A FAN OF HARRY POTTER BEFORE YOU GOT THE PART?
Bonnie: I am definitely as fanatical as many of the other fans out there. I really enjoy the books and I can't wait for the last one.
Evanna Lynch beat 15,000 hopefuls to land the part of Luna Lovegood
Evanna: When I was about eight I was stuck in a phase of reading Tintin books but my mum wanted me to read something else. She said "there is this great book called Harry Potter", but I said I didn't want to read about a boy with glasses - I just thought it sounded silly.
Then she read me a chapter and I took it from her, because I loved it - and Tintin took the bottom shelf.
Matthew: I've been acting since I was five, doing Heartbeat and that kind of thing, and when I got to the age of 11 I had already read the books - I was a massive fan.
I heard they were making a film and I just wanted to be in it in some way. Even just as an extra, it would have been perfect.
HOW DID YOU GET YOUR PART IN THE FILM?
Bonnie: I heard they were auditioning, and I think it was more a case of "why not go for it?".
Matthew (r) is one of the original cast members
I always really enjoyed being in school plays, and the teamwork involved, but when I went I suppose I never really thought I'd get the role. After I got it there was a moment when I thought "can I do this?".
Evanna: I saw a poster advertising open auditions for Luna. Also I had sent tapes to the casting agent saying that I wanted to play her.
When they told me I had it, I couldn't believe it... I was waiting for her to call back and say: "I was only joking!"
I had to keep it quiet for a few days, but when I told my friends they were very, very excited.
Matthew: I took a day off school to go to the open audition in Leeds.
I was in there about two minutes and read a paragraph from the book. About two or three months later they asked me to come down to London for a recall for Neville Longbottom.
From getting to meet Chris Columbus [director of the first two films], to having a screen test, to actually getting the part happened in the space of about two or three days. To get that call was just great. I was jumping up and down on the sofa going crazy.
WHAT WAS YOUR HIGHLIGHT OF FILMING HARRY POTTER AND THE ORDER OF THE PHOENIX?
Harry has to deal with his emotions as well as evil wizards
Matthew: I love comedy, I love making people laugh - but what I really loved this year was tackling the emotional side of Neville.
That was a big challenge for me because Neville has always been a light-hearted, humorous character and I have never had to do anything as deep and emotional as that before.
Katie: Kissing Harry! I was so worried it was going to go wrong and that we would bang heads or something.
I think it was more awkward beforehand knowing it was going to come up, but we had a chat beforehand and had a laugh, asking each other if we'd brushed our teeth.
WHAT HAS IT BEEN LIKE GROWING UP ON SCREEN?
Bonnie: It has definitely made me more confident. When I was younger - I started when I was nine - I was very timid and shy. We have all grown up in it together and are really comfortable with each other.
Bonnie Wright has starred in all of the Harry Potter films
Matthew: Some of us shave now! We come in and the make-up ladies say 'I'm sick of shaving you, will you just do it before you come in?'.
Even if it's just a little bit of bum fluff they have to get rid of it.
HOW HAS HARRY POTTER CHANGED YOUR LIFE?
Bonnie: Sometimes I get recognised and I don't think you can ever get used to that.
Katie Leung's character Cho is Harry Potter's girlfriend
It is always in places you don't expect. You can be on holiday and someone randomly comes up to you. It has made me aware of how big the audience is for Harry Potter.
Matthew: The things I have experienced and the places I have been are just incredible.
I have to spend a lot of time away from home, so I miss my friends a lot. I get quite homesick, but the pros just outweigh the cons.
When I go to parties back home, my friends say "guess what, he's in Harry Potter" because it's a great good way of getting in with girls.
It's a good way to start a conversation but I like to quickly get away from it. There's a little bit more to me than just Harry Potter.
Katie: I had a lot of positive feedback, fan-mail and stuff. I don't get recognised very often, if anything I'm just more confident now. I used to be really shy so it's a really good thing.