Four equations, formulated by James Clerk Maxwell, that together form a complete description of the production and interrelation of electric and magnetic fields.

The statements of these four equations are as follows:

1. Electric field diverges from electric charge.
2. There are no isolated magnetic poles.
3. Electric fields are produced by changing magnetic fields.
4. Circulating magnetic fields are produced by changing electric fields and by electric currents.

Maxwell based his description of electromagnetic fields on these four statements.