Abstract The thermodynamical properties of the adsorption of the first layer of Xe on a Cu(100) surface have been studied by LEED and AES. We show, from the adsorption isotherms, that the adsorbed xenon undergoes a first order 2D gas ⇌ 2D solid phase transition. The presence of impurities and heterogeneities on the surface alters the form of the isotherm in the prestep region, but does not change the phase transition pressure. The value of the latent heat of transformation is 6.2 kcal/mole. The kinetics of adsorption and desorption have been studied using AES. We determined that both the adsorption and desorption are zero order processes. The sticking coefficient has been found to be practically equal to the unity and the value of the activation energy for the desorption is about 6 kcal/mole.