This document provides an overview of Apache Flink, an open-source stream processing framework. It discusses Flink's capabilities in supporting streaming, batch, and iterative processing natively through a streaming dataflow model. It also describes Flink's architecture including the client, job manager, task managers, and various execution setups like local, remote, YARN, and embedded. Finally, it compares Flink to other stream and batch processing systems in terms of their APIs, fault tolerance guarantees, and strengths.