Time perception is a field of study within psychology and neuroscience. It refers to the sense of time, which differs from other senses since time cannot be directly perceived but must be reconstructed by the brain. Humans can perceive relatively short periods of time, in the order of milliseconds, and also durations that are a significant fraction of a lifetime. Human perception of duration is subjective and variable. Some researchers attempt to categorize people by how they differ in their perception of time (see "Personality characteristics" below).

Pioneering work, emphasizing species-specific differences, was done by Karl Ernst von Baer.^{[citation needed]} Experimental work began under the influence of the psycho-physical notions of Gustav Theodor Fechner with studies of the relationship between perceived and measured time.^{[citation needed]} Work with animals conducted by Jakob von Uexküll included measurement of length of momentum in snails.^{[citation needed]}

William J. Friedman also contrasted two theories for a sense of time: