Traditional cellular communication base stations are usually mounted on towers or buildings. They cover large (macro) areas ranging from a fraction of a mile up to a few miles (1 mi = 1.6 km), depending on their transmit power level and antenna directionality. To complement these macro coverage networks, picocells and femtocells provide users with local extensions of cellular communications services. The cells are used for many purposes, most often for closing gaps in service coverage and for providing service in specific areas, such as within buildings. This is done through the use of low-power base stations connecting the local mobile traffic to the cellular operator's network through the existing wired backhaul links such as home cable or digital subscriber line (DSL) connections. This article examines the characteristics of picocells and femtocells, the benefits of using the technology in wireless networks, and examples of current and future picocell and femtocell deployments