David Tong -- What is Quantum Field Theory?

Q&A - Quantum Fields: The Real Building Blocks of the Universe

What is the reason that classical field theory is not used or taught as much as quantum field theory, even though the two have many similarities and classical field theory was developed

What is the difference between a quantum state and a classical state? - Quora

What is The difference between classical and quantum scattering theory? - Quora

What is the difference between the classical ether and (quantum) fields? - Quora

homework and exercises - Proof of causality in free scalar field

David Tong -- Video Lectures on Quantum Field Theory -- University

David Tong -- Video Lectures on Quantum Field Theory -- University

Quantum Field Theory: University of Cambridge

David Tong: Cambridge Lecture Notes on Theoretical Physics

David Tong: Cambridge Lecture Notes on Theoretical Physics