The textbook "Number Theory" offers a comprehensive introduction to number theory and related mathematical disciplines. It is suitable for both students and self-learners and covers a wide range of topics that go beyond the basics of number theory. The structure of the book is divided into two parts: the first part addresses fundamental concepts of number theory and serves as an introduction to the subject. The second part delves deeper into advanced topics and provides detailed explanations of significant mathematical theorems, such as the Hasse-Minkowski theorem and the prime number theorem. Additionally, the character theory of finite groups and the theory of elliptic functions are also discussed. Each chapter includes valuable literature references to support the reader in further studies.