Grafted polymer layers modify the effective interactions between proteins and surfaces resulting in a change of the ability of the proteins to adsorb on the surface. Grafted polymers have a strong effect on both the equilibrium amount of proteins` adsorbed as well as in the kinetics of adsorption. In this talk we will review some of our understanding of the molecular parameters that determine the ability of polymer layers to reduce protein adsorption. We will present a theoretical approach that enables the study of both the kinetics and thermodynamics of adsorption. The predictions of the theory are in excellent quantitative agreement with experimental observations for the adsorption of proteins on surfaces with grafted (short and long) polyethylene oxide. We will show the role of polymer chain length and surface coverage on both the equilibrium adsorption isotherms and the kinetics of protein adsorption. For example, we find that for fixed polymer surface coverage there is a polymer molecular weight above which the equilibrium adsorption becomes independent of polymer chain length. However, the kinetics of protein adsorption depends very strongly on polymer molecular weight under all conditions. The time dependent adsorption is a very complex process due to the changes in the effective surface-protein interactions as the adsorption process progresses. Namely, the changes in the structure of the polymer layer as the proteins adsorb result in large changes in the kinetic process. We will show under what conditions the predicted equilibrium amount of protein adsorbed is finite, however, the time scale for adsorption is so slow that the layer completely prevents protein adsorption for practical purposes. Finally, we will show how chemical modifications of the polymer layer can be used to manipulate the amount, structure and time scale for adsorption and desorption of the proteins from the modified surface.