Electron-electron interactions are at the origin of many exotic electronic
properties of materials which have emerged from recent experimental
observations. The main important phenomena discovered are related with
electronic magnetic properties, which have been quite accessible to Nuclear
Magnetic Resonance techniques. Those specifically permit to distinguish the
orbitals or electronic bands responsible for the magnetism, the metallic
properties and superconductivity and to reveal the physical properties which
are distinct from expectations in an independent electron scheme. The
description of some selected experimental cases permits us to underline the
importance of the technique and to reveal altogether to the reader a wide range
of novel phenomena specific to correlated electron physics.Comment: 30 pages, 18 figure