This concise guide offers a road map for anyone wishing to navigate, understand, or alter the Microsoft Shared Source CLI ("Rotor") code. Written by members of the core team that designed the .NET Framework, this book is for anyone who wants a deeper understanding of what goes on under the hood of the .NET runtime and the ECMA CLI. Microsoft's Shared Source CLI (code-named "Rotor") is the publicly available implementation of the ECMA Common Language Infrastructure (CLI) and the ECMA C# language specification. Loaded with three million lines of source code, it presents a wealth of programming language technology that targets developers interested in the internal workings of the Microsoft .NET Framework, academics working with advanced compiler technology, and people developing their own CLI implementations. The CLI, at its heart, is an approach to building software that enables code from many independent sources to co-exist and interoperate safely. The book is a companion guide to Rotor's code. It provides a road map for anyone wishing to navigate, understand, or alter the Shared Source CLI code. This book illustrates the design principles used in the CLI standard and discusses the complexities involved when building virtual machines. Included with the book is a CD-ROM that contains all the source code and files. After introducing the CLI, its core concepts, and the Shared Source CLI implementation, Shared Source CLI Essentials covers these topics: the CLI type system; component packaging and assemblies; type loading and JIT Compilation; managed code and the execution engine; garbage collection and memory management; and the Platform Adaptation Layer (PAL) - a portability layer for Win32, Mac OS X, and FreeBSD.