Filmmaking’s 180-degree rule is designed to ensure that viewers feel comfortable and oriented in the space the film or video creates. It's a fairly simple rule. If you are filming a scene of two people conversing, you should imagine a straight line running between them – this is your reference line. To follow the rule, you must keep all of your cameras on one side of that imaginary reference line. As long as the shots all come from somewhere on the same side of the line, the audience remains oriented in the space. In every shot of individuals facing each other, one person is always looking camera-left and the other is always looking camera-right.
But what if you’re filming more than two people? The 180-degree rule still applies – it just needs to be modified a little. In this case, think of your scene as a stage play. Just draw your imaginary line where the front of the stage would be, and then be sure to keep your cameras in the seats.
Breaking the 180-degree rule disturbs the viewers’ comfort and creates feelings of chaos or disorder. That doesn't necessarily mean you should never break the rule. You can break the rule by cutting from one side of the line to a shot from the other, as a technique to create these types of feelings intentionally.
There are even ways to bend the 180-degree rule without actually breaking it. For instance, you can cut to a neutral shot before cutting to a shot across the line to reset viewer expectations. You can also move the camera across the line in a single shot, without cutting at all. Bending the 180-degree rule can help you create unique dynamics, set a new tone and elicit particular emotions from the viewer.
Understanding the 180-degree rule lets you know when to follow it, when to break it and when to bend it. Watch the accompanying video for real-world examples from some films you may find familiar.