Most IoT applications are based on a cloud centric architecture. Data collected from sensors and devices are sent to a gateway, which then transfers it to a cloud based IoT platform. For a growing set of IoT applications, including those that are mission critical, latency sensitive, or with high reliability needs, a new architecture is needed. An edge based architecture, with processing performed at the device, or in a gateway near the devices, is now emerging. This article provides an overview of edge or fog computing, and lists some common use cases.