How do people become moral, good people--and, then again, how do they turn into evil ones? Are ethics based on rational thought, emotion, or intuition?
The psychological study of morality has, for many years, been dominated by a cognitive developmental orientation. Such approaches, such as the prominent theorizing of Piaget (1950, 1960) and Kohlberg (1963, 1964, 1968, 1971), stress the cognitive side of morality; they view humans as philosophers, who carefully consider their principles and the facts before offering a moral pronouncement. Recently, alternative perspective have emerged in social psychology and cognitive neuroscience. These views suggest that morality may be more based on intuition, and emotion, rather than the cognitive processes specified by the cognitive-developmentalists.

Topics
Kohlberg's Theory of Moral Development
Gilligan's Stages of the Ethic of Care
Morality as a nonrational and/or physiological process
Morality and the individual: individual differences in morality (values and personality)

Resources:
Kohlberg, L., & Hersh, R. H. (1977). Moral development: A review of the theory. Theory Into Practice, 16(2), 53-59.
Greene, J. D. & Haidt, J. (2002). How (and where) does moral judgment work? Trends in Cognitive Science, 6, 517-523.
Lee, K., & Ashton, M. C. (2005). Psychopathy, Machiavellianism, and Narcissism in the Five-Factor Model and the HEXACO model of personality structure. Personality and Individual Differences, 38, 1571-1582.
Schwartz, S. H., & Rubel, T. (2005). Sex differences in value priorities: Cross-cultural and multimethod studies. Journal of Personality and Social Psychology, 89, 1010-1028. ONLY pp. 1010-1012 and 1020-1023