A theory, proposed by the humanistic psychologist Abraham Maslow, which classifies human needs into five hierarchical categories:

1. Physiological needs, such as air, food, water
2. Safety: secure employment, home, family
3. Love and belonging: in family and among friends
4. Esteem: confidence, respect for and from others
5. Self-actualization: creativity, problem-solving, morality

Needs which fall towards the top of the hierarchy cannot be met until “lower” needs, such as food, employment, and safety, are fulfilled.

I feel that this resource is a very helpful in-depth look at the hierachy of needs: http://honolulu.hawaii.edu/intranet/committees/FacDevCom/guidebk/teachtip/maslow.htm