The electromagnetic interaction is one of the four fundamental forces of physics. As the gravity is slightly experienced in everyday life, so she has long been thoroughly investigated and well understood for over 100 years. The electromagnetic interaction is responsible for most everyday phenomena such as light, electricity and magnetism. It determines, together with the exchange interaction the structure and properties of atoms, molecules and solids.

Starting point of the research was a study of the forces between electric charges. The law of Coulomb of about 1785 is this force between two point-like charges completely analogous to the law of gravitation to. The effect of electric forces on charges removed is described by the concept of the electric field. This is caused not only by electric charges, but also by temporal changes in magnetic fields. This finding is mainly due to Michael Faraday. While static electric charges appear to have nothing to do with the phenomena of magnetism, a moving electric charge turns out to be the cause of a magnetic field, such as Hans Christian Ørsted in 1820 recognized. When moving in this field a second charge, so she learns the laws of classical electrodynamics, a magnetic force is then about the size of the electric force when the relative speed of the order of the speed of light. The classical electrodynamics is the first example of a field theory which satisfies Einstein's principle of relativity. If the electrodynamics would only be invariant under Galilean transformations, then there would be no induction phenomena and no propagation of electromagnetic waves.

The theory of classical electrodynamics goes back to James Clerk Maxwell, who in the Maxwell equations named after him, the laws of electricity, magnetism and light as different aspects of a fundamental interaction of electromagnetism recognized in the 19th century. The electromagnetic interaction which is itself the result of the summary of the theory of electric and magnetic interaction is described since 1967 with the weak interaction together as electroweak interactions. An integration of the strong interaction in the common unified field theory is sought.

It is characteristic of the electromagnetic interaction that it has a large ( in principle infinite) range and at the same time is absättigbar, ie the effect of a negative and a positive charge to a distant third charge stand out practically. The intensity of the electromagnetic interaction is determined by the fine structure constant, this coupling constant is approximately a factor 100 smaller than that of the strong interaction but by several order of magnitude greater than that of the weak interaction, and certainly much higher than that of gravitation.

Phenomena of electromagnetism can also be observed when no electrical charge is present within touching distance, such as electromagnetic waves or the decay of the pion into two gamma - photons.

In the area of the smallest particles, the electromagnetic interaction is described by quantum electrodynamics. The electromagnetic potentials are regarded therein as field operators, through this, the photon, the interaction particles of the electromagnetic interaction, created or destroyed. Clearly this means that the interaction between charged particles, ie the exchange of momentum and energy, the result of the exchange of photons between these particles.