Files with the .UNITY3D extension contain game data archives – namely all resources and other information stored in a closed, proprietary, single-file format. UNITY3D files are created in Unity, a program used to write and release 3D games.

UNITY3D files allow you to start the game in a browser window, provided that the browser has the Unity Web Player plug-in installed. They can be published from the UNITY scene file. Access to proprietary game data is protected.