In psychology, rejection is an emotion felt by most humans (and possibly other higher animals) when another person denies a personal request, particularly if it is an emotional advance. Repeated rejection (particularly of children) or fear of it, can lead to loneliness and depression.

In medicine, transplant rejection usually refers to the immune reaction of a host organism to a foreign biological tissue, such as in a transplantation.

In telecommunications, rejection is the receiving of the desired signal without interference from another undesired one. See selectivity and adjacent-channel rejection .