How to set Unity to 2D mode

As of Unity 4.3.2, when you create a new 2D project, the “screen view” and “editor mode” remain defaulted to 3D. If you’re creating a 2D project you’ll want to update these settings right away. You’ll also want to change the “Main Camera” projection from Perspective to Orthographic.

To change the “editor mode,” goto “Edit” > “Project Settings” > “Editor.” Then, in the “Editor Settings” inspector panel, change the “Default Behavior Mode” to “2D.”

To change the “screen view,” simply toggle the small “2D” button found at the top of the “Scene” panel.

To change the “Main Camera” projection, select “Main Camera” in the “Hierarchy.” Then, in the inspector panel, find the “Projection” dropdown, and change it from “Perspective” to “Orthographic.”

For more information here’s a short-ish Unity tutorial on the differences between 2D and 3D mode.