The Tilt-Shift effect is achieved using a special lens that enables “photographer[s] very exacting control over the depth-of-field in an image, much more than any regular lens could provide. Video after the break. First picture in gallery.

..because tilting the lens with respect to the film/sensor plane changes the perspective in the image: you can make lines that otherwise would converge, showing perspective, instead remain parallel or even diverge

[via Cheapshooter]