In cinema, blurriness is usually intended to go unnoticed. When it appears it is either considered an error – a mistake of focus or a technological failure – or a background effect of shallow focus intended to offset a defined image. As Martine Beugnet argues, however, blur is an essential feature of the cinema, possessing its own properties and affordances, and capable of powerful effects.

Examining an array of notable examples of blurriness from horror to art cinema and experimental film, and including the works of the Lumière brothers, Josef von Sternberg, Agnès Varda and many others, she develops a taxonomy of blurs, from speed and motion blur to the hand-held, "shaky camera" blur common in contemporary digital cinema. These wide-ranging instances all return the viewer to the sensorial and material qualities of the moving image.

In the face of technological developments that valorize sharpness as an indicator of progress, blur stands as a provocative reminder of the value of uncertainty—a sign of the irreducible mystery at the heart of the filmic image.