Pauli’s exclusion principle Wolfgang Pauli (in 1925) discovered the fundamental principle that governs the electronic configuration of atoms with more than one electron by analyzing the data of atomic spectra. The exclusion principle can be stated as,

"No two electrons in an atom can exist in the same quantum state."

In other words no two electrons can have the same set of quantum numbers. This principle is applicable for all fermions (spin 1/2 particles) in any quantum system.