fr:Niveau d'énergie sv:energinivå pl:Powłoka elektronowa

An energy level is a quantified stable energy, which a physical system can have; the term is most commonly used in reference to the electron configuration of electrons, in atoms or molecules. According to quantum theory, only certain energy levels are possible; the higher an electron's level, the greater its potential energy.

The set of all energy levels of a system is called its energy spectrum.

An energy state or molecular energy state is comprised of an electronic, vibrational, and rotational component, such that:

<math>E = E_{electronic}+E_{vibrational}+E_{rotational}<math>

The specific energies of these components vary with the specific energy state and the substance.