Recent progress in dynamical approach to the activated adsorption and its reverse process over well-defined metal surfaces has been reviewed. Experiments monitoring the threshold for the dissociative adsorption and the extent as a function of the incident energy have been made. And this provided information on the height and orientation of the activation barrier as well as the presence of quantum mechanical tunneling through the barrier. The angular distribution of desorbing molecules and the velocity distribution yield a wealth of information on the interaction between the molecules and surfaces. State specific measurements of desorbing molecules are briefly summarized.