The quantum field theory is an area of theoretical physics, in the principles of classic field theory and the quantum mechanics are combined to form an expanded theory. It goes beyond quantum mechanics by uniformly describing particles and fields. Not only so-called observables are quantized, but also the interacting ones fields themselves; Fields and observables are treated analogously.The quantization of the fields is also called second quantization.This explicitly takes into account the formation and annihilation of elementary particles.

The methods of quantum field theory are mainly used in elementary particle physics and in statistical mechanics. A distinction is made here between relativistic quantum field theories, which take into account the special theory of relativity and are frequently used in elementary particle physics, and non-relativistic quantum field theories, which are relevant for example in solid state physics.