The intention of most film editing is to create the impression of continuous action (“continuity”) by presenting discontinuous visual information. The techniques used to achieve this, the continuity editing rules, are well established yet there exists no understanding of their cognitive foundations. This thesis attempts to correct this oversight by proposing that “continuity” is actually what perceptual and developmental psychologists refer to as existence constancy (Michotte, 1955): “the experience that objects persist through space and time despite the fact that their presence in the visual field may be discontinuous” (Butterworth, 1991). The main conclusion of this thesis is that continuity editing ensures existence constancy by creating conditions under which a) the visual disruption created by the cut does not capture attention, b) existence constancy is assumed, and c) expectations associated with existence constancy are accommodated after the cut. Continuity editing rules are shown to identify natural periods of attention withdrawal that can be used to hide cuts. A reaction time study shows that one such period, a saccadic eye movement, occurs when an object is occluded by the screen edge. This occlusion has the potential to create existence constancy across the cut. After the cut, the object only has to appear when and where it is expected for it to be perceived as continuing to exist. This spatiotemporal information is stored in a visual index (Pylyshyn, 1989). Changes to the object’s features (stored in an object file; Kahneman, Treisman, & Gibbs, 1992), such as those caused by the cut, will go unnoticed. A duration estimation study shows that these spatiotemporal expectations distort due to the attention withdrawal. Continuity editing rules show evidence of accommodating these distortions to create perceived continuity from discontinuous visual information. The outcome of this thesis is a scientific understanding of filmic continuity. This permits filmmakers greater awareness of the perceptual consequences of their editing decisions. It also informs cognitive scientists of the potential of film as an analogue for real-world perception that exposes the assumptions, limitations, and constraints imposed upon our perception of reality.