  We discuss the flavor content of the nucleon in an unquenched quark model in
which the effects of quark-antiquark pairs (up, down and strange) are taken
into account in an explicit form. It is shown that the inclusion of
quark-antiquark pairs leads to an excess of anti-d over anti-u quarks in the
proton and to a large contribution of orbital angular momentum to the spin of
the proton.
