Abraham Maslow is known for establishing the theory of a hierarchy of needs, writing that human beings are motivated by unsatisfied needs, and that certain lower needs need to be satisfied before higher needs can be satisfied.

The taxonomy includes different types of needs (physiological, safety, love, and esteem) that must be satisfied before a person can act unselfishly. He called these needs "deficiency needs." As long as we are motivated to satisfy these cravings, we are moving towards growth, toward self-actualization. Satisfying needs is healthy, blocking gratification makes us sick or evil. In other words, we are all "needs junkies" with cravings that must be satisfied and should be satisfied. Else, we become sick.

Needs	Demonstrated
Self-Actualization	The need for self-actualization is "the desire to become more and more what one is, to become everything that one is capable of becoming." People who have everything can maximize their potential. They can seek knowledge, peace, esthetic experiences, self-fulfillment, oneness with God, etc. It is usually middle-class to upper-class students who take up environmental causes, join the Peace Corps, go off to a monastery, etc.
Esteem Needs	There are two types of esteem needs. First is self-esteem which results from competence or mastery of a task. Second, there's the attention and recognition that comes from others. This is similar to the belongingness level, however, wanting admiration has to do with the need for power. People who have all of their lower needs satisfied, often drive very expensive cars because doing so raises their level of esteem. "Hey, look what I can afford-peon!"
Love Needs	Love and belongingness are next on the ladder. Humans have a desire to belong to groups: clubs, work groups, religious groups, family, gangs, etc. We need to feel loved (non-sexual) by others, to be accepted by others. Performers appreciate applause. We need to be needed. Beer commercials, in addition to playing on sex, also often show how beer makes for camaraderie. When was the last time you saw a beer commercial with someone drinking beer alone?
Safety Needs	Safety needs have to do with establishing stability and consistency in a chaotic world. These needs are mostly psychological in nature. We need the security of a home and family. However, if a family is dysfunction, i.e., an abusive husband, the wife cannot move to the next level because she is constantly concerned for her safety. Love and belongingness have to wait until she is no longer cringing in fear. Many in our society cry out for law and order because they do not feel safe enough to go for a walk in their neighborhood. Many people, particularly those in the inner cities, unfortunately, are stuck at this level. In addition, safety needs sometimes motivate people to be religious. Religions comfort us with the promise of a safe secure place after we die and leave the insecurity of this world.
Physiological Needs	Physiological needs are the very basic needs such as air, water, food, sleep, sex, etc. When these are not satisfied we may feel sickness, irritation, pain, discomfort, etc. These feelings motivate us to alleviate them as soon as possible to establish homeostasis. Once they are alleviated, we may think about other things.