  The heavy fermion properties are reviewed on selected examples often studied
in Grenoble. The physical problems are presented as example of exotic matter at
low temperature with three major insights: the localisation of the 4f
electrons, the collapse of the long range magnetic order and the entrance in an
intermediate valence regime. The question on the first or second order nature
of the quantum phase transition will be discussed. In the first example, the
Ising Kondo lattice of CeRu2Si2, experiments seem to be described with the
picture of 4f itinerant electron dominated by their spin fluctuations; the
strong feedback, induced in magnetic field, between magnetostriction and switch
in the nature of the magnetic interactions illustrates the proximity of a
quantum critical field. Comparison is made with CeCu6 or YbRh2Si2 series where
the idea of local criticality seems to emerge. Basic arguments are discussed
for the breakdown of the idea that Yb heavy fermion systems are the the hole
analogue of the cerium ones. Special focus is given on the interplay between
unconconventional superconductivity and magnetism either for dominant
antiferromagnetic or ferromagnetic correlations. Huge electronic Gruneisen
parameter leads often to strong concomitant 4f density and spin fluctuations
>.The main boost given by the discovery of new materials as quasi-bidimensional
Ce 115 compounds or recently by CePt3 Si or skutterudites is spectacular for
the theoretical developments. Finally, the now canonical cases of the UPt3,
URu2Si2, UPd2Al3 and UBe13 give now a sound basis in the rich domain of
unconventional superconductors.
