Quantum electrodynamics, or QED, is a quantum field theory of electromagnetism. QED describes all phenomena exhibited by charged point particles, such as electrons and positrons, and the particles of light (photons), interacting by electromagnetism. This theory includes classical electrodynamics in the limit of large fields, but also explains purely quantum phenomena such as the structure of atoms and molecules, creation of particles by electromagnetic field, and the anomalous magnetic moment of the electron. (The latter prediction has been experimentally confirmed to 11 decimal digits.)
QED was was the first quantum field theory in which the difficulties of building a consistent, fully quantum description of fields and creation and annihilation of quantum particles were satisfactorily resolved. R. P. Feynman, J. Schwinger and S. Tomonaga received a 1964 Nobel prize in physics for its development.
Literature: R. P. Feynman. QED: A strange theory of light and matter.