Have you ever stopped to think about all the things that have to take place when you execute a .NET program? As the quote from Neal Ford says "Understand one level below your usual abstraction", this talk will look at why this is important and how can it help you if we apply it to the .NET framework. We will delve into the internals of the recently open-sourced .NET Core Runtime, looking at what happens, when it happens and why. Using freely available diagnostic tools such as PerfView, libraries including ClrMD and even the source code itself! Along the way we'll examine the Execution Engine, Type Loader, Just-in-Time (JIT) Compiler and the CLR Hosting API, to see how all these components play a part in making a 'Hello World' app possible.