Understanding the behavior of enzymes at solid surfaces requires coping with the complexity of the interfaces. Examples are given to illustrate key considerations: (i) influence of the adventitious contamination; the amount of glucose oxidase adsorbed on stainless steel in conditions producing an electrochemical effect is very low compared to the amount of organic contaminants; (ii) structure (multilayered, random) of an adsorbed phase containing an enzyme and other organic constituents (self-assembled monolayer, adventitious contaminants); (iii) competition between proteins for adsorption and influence of the adsorption procedure (simultaneous or sequential) and (iv) reality vs. expectation in enzyme (glucose oxidase) immobilization by tentative covalent grafting. The study of enzyme adsorption in several model systems (catalase on surface-modified carbon blacks, beta-glucosidase on clay at different pHs, beta-glucosidase on sand and surface-modified sand) showed that a strong adsorption, whether by electrostatic or hydrophobic interactions, provokes an extensive deactivation. After adsorption, which is a quick process, the enzyme activity may continue to decrease both in the adsorbed phase and in the solution owing to dynamic processes which involve the adsorbed enzyme and exchanges between the adsorbed phase and the liquid phase. (c) 2008 Elsevier Ltd. All rights reserved.