There's perhaps no better example of sustained attention on a single computing task than when people are engaged playing a digital game or watching a film or TV show. This state is frequently described as immersion. Our work on immersion provides insight into the experiences people have when playing videogames or when watching films. We have explored what it means when players say they are immersed in a game, the factors that influence the degree of engagement experienced, and ways in which to measure that level of engagement.