In this paper, it is argued, based on evidence from psychological literature, that there are three major approaches to the study of personality, namely (a) situationism, (b) interactionism, and (c) constructivism. It is also noticed that these approached have resulted in the emergence of three major types of personality theories: (1) type theories, (2) trait theories, and (3) factor theories. In connection to TESOL, it is argued that extroversion/introversion and risk-taking are the most important personality factors. It is also argued that such personality factors as tolerance of ambiguity, empathy, self-esteem, inhibition, and intelligence have also been addressed by TESOL research, but that the two most important factors are extroversion/introversion and risk-taking.