Mourning is the expression of an experience that is the consequence of an event in life involving loss, causing grief, occurring as a result of someone's death, specifically someone who was loved although loss from death is not exclusively the cause of all experience of grief.

The word is used to describe a complex of behaviours in which the bereaved participate or are expected to participate, the expression of which varies by culture. Wearing black clothes is one practice followed in many countries, though other forms of dress are seen. Those most affected by the loss of a loved one often observe a period of mourning, marked by withdrawal from social events and quiet, respectful behavior. People may follow religious traditions for such occasions.

Mourning may apply to the death of, or anniversary of the death of, an important individual such as a local leader, monarch, religious figure, or member of family. State mourning may occur on such an occasion. In recent years, some traditions have given way to less strict practices, though many customs and traditions continue to be followed.