This document provides an overview of the past, present, and future of Apache Hadoop YARN. It discusses how YARN has evolved from Apache Hadoop 2.6/2.7 to now support 2.8 with features like dynamic resource configuration, container resizing, and Docker support. Upcoming work includes support for arbitrary resource types, federation of multiple YARN clusters, and a new ResourceManager UI. The future of YARN scheduling may include distributed scheduling, intra-queue preemption, and scheduling based on actual resource usage.