This document provides an introduction to OpenDaylight, an open source platform for Software-Defined Networking (SDN). It outlines what OpenDaylight is, its community and releases, the components within OpenDaylight including northbound and southbound interfaces, and some example network applications that can be built on OpenDaylight. It also provides an overview of how to develop applications using OpenDaylight, covering technologies like OSGi, MD-SAL, and the Yang modeling language.