A need is dissatisfaction at a point of time and in a given context. Needs are distinguished from wants. In the case of a need, a deficiency causes a clear adverse outcome: a dysfunction or death. In other words, a need is something required for a safe, stable and healthy life (e.g. air, water, food, land, shelter) while a want is a desire, wish or aspiration. When needs or wants are backed by purchasing power, they have the potential to become economic demands.

Basic needs such as air, water, food and protection from environmental dangers are necessary for an organism to live. In addition to basic needs, humans also have needs of a social or societal nature such as the human need to socialise or belong to a family unit or group. Needs can be objective and physical, such as the need for food, or psychical and subjective, such as the need for self-esteem. The concept of "unmet need" arises in relation to needs in a social context which are not being fulfilled.

Needs and wants are a matter of interest in, and form a common substrate for, the fields of philosophy, biology, psychology, social science, economics, marketing and politics.