We can download Unity3D from the Unity3D website (http://unity3d.com/unity/download/).
Before we download it, it is a good idea to check the requirements to make sure that our system (that is, software and hardware) is up-to-date. We can visit http://unity3d.com/unity/system-requirements to check whether our system complies with the requirements. Once we have checked the requirements, we can download the latest version of Unity3D for either Mac OS (http://unity3d.com/unity/download/download-mac) or Windows (http://unity3d.com/unity/download/download-windows). Opening either of these URLs will start the download of Unity3D automatically.
While the latest version of Unity3D is available on the official website, it is also possible to download previous versions of Unity3D from the following link: http://unity3d.com/unity/download/archive. If we use this book as a support for a course, it may be the case that the college or university where we study may have a previous version installed in the labs, and we may want to work on the project we have created during class from home. Another reason for this is that when we open a Unity3D project with a new version of the software, we may not be able to reopen it with the previous version.
Once we have downloaded Unity3D, launch the installer.