These lectures were given in the framework of the ``Dixi\`eme s\'eminaire
rhodanien de physique'' entitled ``Le spin en physique'', given at Villa
Gualino, Turin, March 2002. We have shown how the difficulties of
interpretation of atomic spectra led to the Pauli exclusion principle and to
the notion of spin, and then described the following steps: the Pauli spin with
2×2 matrices after the birth of "new" quantum mechanics, the Dirac
equation and the magnetic moment of the electron, the spins and magnetic
moments of other particles, proton, neutron and hyperons. Finally, we show the
crucial role of statistics in the stability of the world.Comment: latex file, 7 figures, 3 table