Enzymes are extremely useful in many industrial and pharmaceutical areas due to their ability to catalyze reactions with high selectivity. In order to extend their lifetime, significant efforts have been made to increase their stability using protein- or medium engineering as well as by chemical modification. Many researchers have explored the immobilization of enzymes onto carriers, or entrapment within a matrix, framework or nanoparticle with the hope of constricting the movement of the enzyme and shielding it from aggressive environments, thus delaying the denaturation. These strategies often balance three competing interests: (i) maintaining high enzymatic activity, (ii) ensuring good long-term stability against temperature, dehydration, organic solvents, and or aggressive pH, and (iii) enabling a tuning or reversible switching of enzyme activity. In most cases, multiple enzymes will be contained within a single nanoparticle or matrix, but in recent years researchers have begun to wrap up individual enzymes within single enzyme nanoparticles (SENs). In these nanoparticles the enzyme is stabilized by a thin shell, typically a polymer, prepared either by in situ polymerization from the enzyme surface or by assembling a preformed polymer around it. Because of the increased control over the environment directly around the enzyme, and the possibility of more directly controlling substrate diffusion, many SENs show remarkable stability while retaining high initial activities even for quite fragile enzymes. Moreover, the activity of the enzyme can often be more easily fine-tuned by adjusting the layer properties. We postulate that this emerging field will offer exciting and elegant opportunities to both extend the catalytic lifetime of enzymes in aggressive solvents, temperatures and pH, and enable their activity to be switched on and off on demand by modulation of the outer material layer.