This Is 40 premieres at Grauman's Chinese Theatre tonight! Stars from the movie (Leslie Mann, Paul Rudd, Megan Fox, Jason Segel, Albert Brooks, Robert Smigel and other cast members) and writer/director/producer Judd Apatow are all scheduled to start walking the red carpet at 6:00 p.m. If you're planning on attending for celebrity spotting, I highly recommend arriving early.
Grauman's Chinese Theatre is located at 6925 Hollywood Boulevard and directions can be found here. You can park at Hollywood & Highland Center for 4 hours for $2.00 after validation (which you can get at the information booth without having to purchase anything).