Emma Watson
C/O Harry Potter Productions
Leavesden Studios
P.O Box 3000
Leavesdon, Hertfordshire
WD2 7LT
United Kingdom

Hermione Granger
C/O Warner Bros
4000 Warner Blvd
Burbank, CA 91522



Emma Watson
C/O PFD
Drury House 34-43
Russel Street
London WC2B 5HA
United Kingdom

They mentioned to send a prepaid envelope along with your letter because that doubles your chance of getting a reply... yeah, and they also said to make sure it's not longer than one page. (dang it! lol)