Drivers for Ubuntu are available on the Linux distribution's own website, as well as other Linux and open source websites such as Linux Drivers and Sourceforge. However, while some drivers are proprietary, Ubuntu has the ability to support nearly all modern devices using the drivers bundled with the operating system.
Ubuntu's creators place a special emphasis on using free and open source software wherever possible. While free software is simply any software application whose creators or owners give it away free of charge, open source software uses an even less restrictive model. Open source software is not only given to users free of charge, it also allows users to make any modifications to the software's source code. Open source software further allows anyone who modifies the original software to give away or sell their modified version in whatever way they choose.
Drivers for some pieces of hardware are proprietary software. Proprietary software is owned by a copyright holder, and it therefore cannot be used without an official license. Aside from using the software without a license, modifying proprietary software without expressed permission from its copyright holder is also a copyright violation.
While Ubuntu did not initially include any proprietary drivers, more of these drivers have been added to the operating system over the years. While this impinges on Ubuntu's free software philosophy somewhat, it also makes Ubuntu more appealing to users who might not otherwise consider using Linux.