Lots of people seem to be asking the question: What is transmedia storytelling?
In short you could say that transmedia storytelling is storytelling across platforms that allows for the user to take part in the storytelling. Instead of using only one platform transmedia storytellers create a much more far-reaching story world that spreads across platforms.
In Wired Magazine we found an interesting article with a good example of transmedia storytelling. Click the front cover below and get redirected to the article.