Textbook in PDF format This book is designed as an introductory course in Quantum Field Theory (QFT) for students who have completed two full graduate-level courses in Quantum Mechanics (QM). Quantum Field Theory is the framework that combines quantum mechanics with special relativity, providing a comprehensive description of fundamental forces and particles. It is a crucial part of modern theoretical physics and essential for understanding the behaviour of elementary particles, the dynamics of fields, and the interactions that govern the universe at the smallest scales. This book is structured to gradually introduce the key concepts and mathematical tools necessary for mastering QFT. Each chapter builds on the knowledge acquired in previous sections, ensuring a coherent and comprehensive understanding of the subject. The material presented here helps doctoral students bridge the gap between the traditional quantum mechanics taught at the graduate level and the more advanced concepts and techniques used in quantum field theory