You set up a list of movies you want in Netflix so that when you send one back, they know what to send out in its place. Your queue can be as long as you want it to be (get your head out of the gutter) and you can add movies, delete them, and reorder the list anytime you want. If you make a request for a movie that's not available yet (not released), it will list them with a disclaimer that it won't be available until such and such date. If a release date has not been announced, you add it to a different queue that lists all those you want to add when they are announced. When announced, they are added to your queue. It's really quite handy.