As I wrote in the April 11, 2006 Roland’s Ramblings there is a hierarchy of needs according to Abraham Maslow.
According to Maslow’s theory of motivation, there are five human needs that humans seek. As a person attempts to fill those needs, one level must be met before the next level, sort of like in a stepping stone with one building upon the next. The five needs in order of progression are: Physiological (air, water, food, sleep); Safety (shelter, danger-free); Belonging (love, affection); Esteem (confidence, self-esteem, respect from others); and, Self-Actualization (achieving full personal potential ).
I would like to suggest you read The Five Levels of Maslow’s Hierarchy of Needs from the Psychology pages of About.com. You also may be interested in reading Maslow’s Hierarchy from ChangingMinds.org.
Also, check out the Wikipedia Abraham Maslow article.