Agreeableness is a tendency to be pleasant and accommodating in social situations. In contemporary personality psychology, agreeableness is one of the five major dimensions of personality structure, reflecting individual differences in concern for cooperation and social harmony. People who score high on this dimension are empathetic, considerate, friendly, generous, and helpful. They also have an optimistic view of human nature. They tend to believe that most people are honest, decent, and trustworthy.
People scoring low on agreeableness are generally less concerned with others' well-being, report less empathy, and are therefore less likely to go out of their way to help others. Their skepticism about other people's motives may cause them to be suspicious and unfriendly. People very low on agreeableness have a tendency to be manipulative in their social relationships. They are more likely to compete than to cooperate.
Agreeableness is considered to be a superordinate trait, meaning that it is a grouping of more specific personality traits that cluster together statistically. There are exceptions, but in general, people who are concerned about others also tend to cooperate with them, help them out, and trust them. This dimension of personality was initially discovered in research using the method of factor analysis.
Agreeableness can be viewed as the opposite of Machiavellianism. It is also similar conceptually to Alfred Adler's idea of social interest.