  Adsorption of charged polymers (polyelectrolytes) from a semi-dilute solution
to a charged surface is investigated theoretically. We obtain simple scaling
laws for (i) the amount of polymer adsorbed to the surface, Gamma, and (ii) the
width of the adsorbed layer D, as function of the fractional charge per monomer
p and the salt concentration c_b. For strongly charged polyelectrolytes (p<1)
in a low-salt solution, both Gamma and D scale as p^{-1/2}. In salt-rich
solutions D~c_b^{1/2}/p whereas the scaling behavior of Gamma depends on the
strength of the polymer charge. For weak polyelectrolytes (p<<1) we find that
Gamma~p/c_b^{1/2} while for strong polyelectrolytes Gamma~c_b^{1/2}/p. Our
results are in good agreement with adsorption experiments and with numerical
solutions of mean-field equations.
