  We propose a new approach to the Kondo lattice in order to describe
simultaneously the Kondo effect and the local magnetism. This approach relies
on an original representation of the $S=1/2$ impurity spin in which the
different degrees of freedom are represented by fermionic as well as bosonic
variables. The magnetic instability is found at $J_c/D =0.67$ in definite
improvement compared to usual fermionic mean- field theories. The dynamical
susceptibility contains an inelastic peak in addition to the standard
Lindhard-type Fermi liquid contribution. The Fermi surface sum rule includes
$n_c+1$ states corresponding to large Fermi surfaces.

Strongly Correlated Electrons