  The flavor content of nucleon form factors is analyzed using two different
theoretical approaches. The first is based on a phenomenological two-component
model in which the external photon couples to both an intrinsic three-quark
structure and a meson cloud via vector-meson dominance. The flavor content of
the nucleon form factors is extracted without introducing any additional
parameter. A comparison with recent data from parity-violating electron
scattering experiments shows a good overall agreement for the strange form
factors.
  A more microscopic approach is that of an unquenched quark model proposed by
Geiger and Isgur which is based on valence quark plus glue dominance to which
quark-antiquark pairs are added in perturbation. In the original version the
importance of $s \bar{s}$ loops in the proton was studied. Here we present the
formalism for a new generation of unquenched quark models which, among other
extensions, includes the contributions of $u \bar{u}$ and $d \bar{d}$ loops.
Finally, we discuss some preliminary results in the closure limit.
