Maslow's primary contribution to psychology is his "Hierarchy of Human Needs", which he often presented as a pyramid, with self-actualization at the top as the highest of those needs. The base of the pyramid is the physiological needs, which are necessary for survival. Once these are taken care of, an individual can concentrate on the second layer, the need for safety and security. The third layer is the need for love and belonging, followed by the need for esteem. Finally, self-actualization forms the apex of the pyramid.
In this scheme, the first four layers are what Maslow called "Deficiency Needs or D-needs." If they are not filled, you feel anxiety and attempt to fill them. If they are filled, you feel nothing; you feel only the lack. Each layer also takes precedence over the layer above it; you do not feel the lack of safety and security until your physiological needs are taken care of, for example. In Maslow's terminology, a need does not become salient until the needs below it are met.
Needs beyond the D-needs are "Growth Needs", "Being Values" or "B-needs". When fulfilled, they do not go away, rather, they motivate further. He outlines about 14 of these values or B-needs, including beauty, meaning, truth, wholeness, justice, order, simplicity, richness, etc.
