The study of personality traits is useful for identifying the numerous variables that exist from human to human; combinations of these variables provide us with a true level of individuality and uniqueness. In the field of psychology, trait theory is considered a key approach to the study of human personality (Crowne, 2007; Burton, Westen & Kowalski, 2009). This article aims to identify a number of significant contributors who have played crucial roles in both the development and application of trait theory. This article then shifts focus to these theorists, outlining their theory and analyzing both the strengths and weaknesses of those theories. An illustration of the methods used in measuring traits is provided and includes arguments both for and against such procedures. Finally, the results of the trait theory and its components described in the article will be summarized. Major contributors to personality trait theory include three eminent psychologists. Boeree (2006) states that the American psychologist Gordon Allport has been described as the founding father of personality trait theory. Allport's distinguished career saw him serve as president of the American Psychological Association (APA) and receive the Gold Medal Award and the Distinguished Scientific Contribution Award from the APA (Carducci, 2009, p. 260). After meeting Sigmund Freud in 1922 and studying his interpretation of personality, Allport developed the opinion that psychoanalysis was too thorough while behaviorism was too superficial in the field of personality psychology. It was this insight that led Allport to develop his own theory of personality (Ewen, 2003, p. 260). According to Ewen (2003), in 1936 Allport used only one dictio...... middle of paper......Lynam, DR, Caspi, A., Moffitt, TE, Raine, A., Loeber, R . , & Stouthamer-Loeber, M. (2005). Adolescent psychopathy and the Big Five: Results from two samples. Journal of Abnormal Child Psychology, 33, 431–443. Magnavita, J. J. (2002). Personality theories: Contemporary approaches to personality science. New York: Wiley.Matthews, G., Deary, I. J., & Whiteman, M. C. (2009). Personality traits. Cambridge, UK: Cambridge University Press.McCrae, R.R., & Allik, IU (2002). The five-factor model of personality across cultures. New York: Kluwer Academic/Plenum Publishers. Nairne, J. S. (2009). Psychology. Australia: Thomson/Wadsworth. Srivastava, S. K. (2005). Organizational and managerial behavior. New Delhi: Sarup & Sons. Tucker, W. H. (2009). The Cattell Controversy: Race, Science, and Ideology. Urbana: University of Illinois Press.