This book describes C # version 3.0. It is divided into two parts. Part I provides a detailed explanation of the C # language, including the new properties introduced in version 3.0. This is the largest part of the book, which describes the keywords and properties of this language, as well as I/O and file processing operations, reflection and preprocessor. Part II discusses the C # class library, which is also a class library for the .NET Framework. This library is quite extensive, but due to the lack of space in this book, it is simply impossible to describe it in full. Therefore, Part II focuses on the root library, which resides in the System namespace.