http://www.diffen.com/difference/GNOME_vs_KDE

GNOME, KDE and Xfce are the most popular desktop environments for Linux. Most people end up using the default desktop environment that ships with their preferred Linux distribution. But experienced users prefer one over the year for either usability, performance, design or customizability considerations.

GNOME began as a project to develop a free and open-source desktop environment and corresponding applications in August 1997. Its design philosophy can be best described as streamlined and easy to use.

KDE community started in October 1996. Its design philosophy is dedicated to functionality and expansion of its features.