Vigilance is a term used in modern psychology to describe the ability to maintain concentrated attention over prolonged periods of time). During this time, the person attempts to detect the appearance of a particular target stimulus. The study of vigilance has expanded since the 1940s mainly due to the increased interaction of people with machines for applications involving monitoring and detection of rare events and weak signals). Vigilance decrement is defined as "deterioration in the ability to remain vigilant for critical signals with time, as indicated by a decline in the rate of the correct detection of signals").

Outside of psychology, vigilance refers to the quality or state of being vigilant, which means watchfulness or careful attention, especially in order to notice possible danger. Examples of vigilance in everyday life include maintaining vigilance while driving, being vigilant for small signs of discomfort in conversation, and practicing vigilance and responsibility in daily life.

In a medical setting, vigilance is sometimes used to mean "insomnia".