Elementary OS is a Linux distribution that comes with its own desktop environment called Pantheon. The developers do not officially support installing Pantheon separately from the rest of the distribution. In fact, while Elementary OS Freya is based on Ubuntu 14.04, it requires newer versions of several packages.

Fortunately, if your computer is already running Ubuntu 14.04, there is a reasonably easy way to transform your existing setup into a seemingly genuine Elementary OS setup.