Adaptive compilation and runtime in the OpenJDK Hotspot VM offers significant performance enhancements for our tools and applications in Java and other JVM languages. Understanding how it works provides developers with critical information on the Java HotSpot JIT compilation and runtime techniques such as vectorization, compressed OOPs etc., to assist in understanding performance for both client and server applications. We will focus on the internals of OpenJDK 8, the reference implementation for Java SE8.