Proteins are large, amphiphilic molecules and as such are highly surface-active: they seek out the interfacial environment. Proteins will thus tend to accumulate at any gas-liquid or solid-liquid interface, and in doing so their biological activity is often altered. Such behavior has consequences for many areas of science and technology where protein-containing fluids are present. Examples are protein separation and purification, the "biofouling" of surfaces in bioprocess equipment and biosensors, and the biocompatibility of medical devices such as vascular prostheses and contact lenses. In the case of biocompatibility, the adsorbed proteins determine subsequent cell interactions. A theme which emerges from these considerations is the need to be able to "control" or "direct" protein adsorption. In this presentation the interfacial behavior of proteins will first be discussed. Approaches to the control of protein adsorption will then be suggested. Such control has a number of aspects, including selecting a given protein from a multiprotein fluid (eg blood), controlling the conformation (and thus the function) of adsorbed proteins, and preventing adsorption altogether. Examples from the author's research in the blood compatibility area will be presented. These will include fibrinolytic (clot-dissolving) surfaces based on the preferential adsorption of plasminogen, anticoagulant surfaces based on thrombin scavenging, and protein repellent surfaces based on polyethylene oxide grafting.