We have experimentally studied the adsorption of polyelectrolytes at oppositely charged surfaces. A weak flexible polyelectrolyte, poly( acrylic acid), was adsorbed from dilute solutions on a Langmuir film of a cationic amphiphile, dimethyldioctadecylammonium bromide. The polymer surface coverage,, at equilibrium was measured by two reflectivity techniques-ellipsometry and polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS) sas a function of the surface charge density, sigma, and of the polymer ionization degree, R. Different adsorption regimes were evidenced. For weakly charged surfaces, sigma < sigma(sat), increases with sigma and with 1/alpha, as expected for a neutralization of the surface by the adsorbed polymers. For highly charged surfaces, sigma > sigma(sat), the adsorption of polyelectrolytes saturates. The mean orientation of the adsorbed chains also depends on the value of sigma: it is parallel to the surface for sigma < sigma* (< sigma(sat)) and orthogonal to the surface for sigma > sigma*. We have measured the values of sigma(sat) and sigma* as a function of R and compared the results with existing theories.