Marketing of a large budget film

After spending millions of dollars on making a movie, the studio spends millions more on letting audiences know about it. Marketing a big product like a movie can be a very expensive business, especially when that product has a limited shelf life. Movies have to be a hit on their opening weekend, often on their opening day, otherwise they tend to disappear very quickly, and the studio stands to make a loss on their investment. Most blockbuster movies already have an audience. The studio has greenlit a huge budget for the movie because they already know people will go and see it - often because it is based on a media text that already has an audience. This may be a previous film (eg Iron Man 2's audience consists of many people who are fans of the first movie), or the source material (the first Iron Man is based on the Marvel character of the same name created by Stan Lee in 1963). This is why remakes and reboots are so popular. Original movies like INCEPTION and AVATAR are the exception to the rule, and represent a huge risk for the studio backing them. Studios have a huge operating overhead, and put out a lot of flops that make no money at all, so they need a guarantee that a blockbuster movie is going to be make not just a small profit, but a comfortable one. After spending $100 million dollars on a movie they can spend 50% as much again (or more) on marketing.