The book "Qt 4.5. Professional programming in C++" describes in detail the development of applications for Windows, as well as Mac OS X and Linux with direct use of the Qt library version 4.5. Here, the capabilities provided by this library are examined in detail, and the characteristic features that distinguish it from other similar libraries are described. This book describes the Qt Creator development environment, and also contains useful information about Qt 4 classes and tips for using them in practice, which are commented in detail with many examples. It should be noted that the disk included with the book contains the texts of the examples specified in the book, the Qt 4.5 library itself and the built-in development environment Qt Creator.