This article outlines the key challenges of mass femtocell deployment as they relate to RF. However, to start off we need to establish a common baseline of understanding by defining what a femtocell is and why such widespread interest in femtocells exists. To avoid confusion we will leverage the definition of a femtocell—or home base station—as provided by the Femto Forum chairman, Simon Saunders, at the 2nd International Conference on Home Access Points and Femtocells. (The Femto Forum is a non-profit organization committed to the standardization and adoption of femtocell technology whose members include leading femtocell players such as Continuous Computing, picoChip and RadioFrame Networks.)