When creating a new project, you can specify whether to start the Unity Editor in 2D mode or 3D mode. However, you also have the option of switching the editor between 2D Mode and 3D Mode at any time. You can read more about the difference between 2D and 3D projects here. This page provides information about how to switch modes, and what exactly changes within the editor when you do.
Switching Between 3D and 2D Modes
To change modes between 2D or 3D mode:
Bring up to the Editor Settings Inspector, via the Edit>Project Settings>Editor menu.
Then set Default Behavior Mode to either 2D or 3D.
You can find out more about the Editor Settings Inspector on the Editor Settings page.
2D vs 3D Mode Settings
2D or 3D mode determines some settings for the Unity Editor. These are listed below.
In 2D Project Mode:
Any images you import are assumed to be 2D images (Sprites) and set to Sprite mode.
The Sprite Packer is enabled.
The Scene View is set to 2D.
The default game objects do not have real time, directional light.
The camera’s default position is at 0,0,–10. (It is 0,1,–10 in 3D Mode.)
The camera is set to be Orthographic. (In 3D Mode it is Perspective.)
In the Lighting Window:
Skybox is disabled for new scenes.
Ambient Source is set to Color. (With the color set as a dark grey: RGB: 54, 58, 66.)
Precomputed Realtime GI is set to off.
Baked GI is set to off.
Auto-Building set to off.
In 3D Project Mode:
Any images you import are NOT assumed to be 2D images (Sprites).
The Sprite Packer is disabled.
The Scene View is set to 3D.
The default game objects have real time, directional light.
The camera’s default position is at 0,1,–10. (It is 0,0,–10. in 2D Mode.)
The camera is set to be Perspective. (In 2D Mode it is Orthographic.)