In Harry Potter's world, it's only been a year since he and his friends were last at Hogwarts School of Witchcraft and Wizardry. In the real world, it's been nearly two years since we've seen their adventures on the big screen.

Production problems — some of them caused by the lengthy, often-nasty Screenwriters Guild of America strike — and other bumps in the road have delayed the release of "Harry Potter and the Half-Blood Prince," based on author J.K. Rowling's sixth novel in the series. Originally, the film was scheduled for a Thanksgiving 2008 release. But it's finally being released July 15. (Several theaters will host midnight screenings July 14.)

The delays haven't quelled Potter-mania at all, though.

In fact, online ticketing sites such as Fandango and Movietickets.com are reporting that pre-sales for the sixth film are so brisk that it may conjure up some serious box-office magic. "Half-Blood Prince" is expected to provide stiff competition for the year's biggest film so far, the second "Transformers" movie.

So before the movie is released, here's a helpful primer to bring you up to speed.

By the way, the filmmakers are already in pre-production for the adaptation of the seventh and final book, "Harry Potter and the Deathly Hallows." It will be split into two movies, the first of which is already scheduled for release Nov. 19, 2010. The second movie will be released July 15, 2011.

The main characters

Harry Potter (Daniel Radcliffe): The boy wizard with a lightning-bolt-shaped scar may be the only person who can stop the Dark Lord Voldemort, who murdered the boy's parents.

Over the course of his studies at Hogwarts, he has grown as a wizard and as a person, and he has found father figures in professor Albus Dumbledore, Sirius Black and the giant Rubeus Hagrid.

Hermione Granger (Emma Watson): Harry's female pal from a supposedly non-magical family also has come into her own. And she's come to have certain feelings for their mutual friend, Ron Weasley.

Ron Weasley (Rupert Grint): Speaking of Weasley, he's overcome his lack of confidence and has become much less bumbling than he was at first. Ron is also trying to deal with his own, conflicting feelings for Hermione.