Bacterial and viral infections of the nail unit are very common as primary infections, especially bacterial paronychia and warts, but they can also be superinfections complicating other nail disorders. In many nail unit infections, the clinical presentation is nonspecific: in these cases, diagnostic tests are mandatory before treatment, to avoid spread of the infection and drug resistance. The most common forms of bacterial and viral infections that may affect the nail unit are herein described in detail, with diagnostic and treatment options provided.