This book is aimed at readers who have their first exposure to quantum field theory. It offers conceptual foundation and application skills in the basics of quantum field theory. It deals with quantum electrodynamics applying operator methods. Still, it provides a modern approach to quantum field theory i.e. to understand even successful theories, like quantum electrodynamics, as "effective field theories". It has sufficient material for a one-semester introductory course and well-suited for self-study. Chapters such as "Towards fields" and "Towards quantisation of fields", offer a lucid introduction for the beginners. All the intermediate steps are displayed throughout. Additional features include, learning outcomes at the end of each chapter, worked exercises throughout and problems at the end of the chapters. The book contains several tables to compare and contrast concepts and also includes necessary background materials. Some chapters/sections can effectively be used as supplementary material in courses such as theory, and advanced statistical mechanics. Special topics discussed include unitary irreducible representation of the Poincare group, Majarona field quantisation, Kallen-Lehmann spectral representation, modern interpretation of renormalization, and outline of effective field theory. Contents: 1 Relativity and One-Particle States 2 Towards Fields 3 Elements of Classical Field Theory 4 Towards Quantisation of Fields 5 Quantisation of The Scalar Field 6 Scattering Theory 7 Lorentz and Poincare Group Representations 8 Quantisation of Spinor Fields 9 Quantisation of Vector Fields 10 Discrete Symmetries 11 Lowest Order Processes of QED 12 Formal Developments 13 Introducing Regularization and Renormalization 14 QED: One-Loop Renormalization15 General Renormalization Theory 16 The Renormalization Group