“Cognitive dissonance” is a frequent occurrence in our daily life. However, less than 1% of the studies of cognitive dissonance have also investigated individuals’ personality traits. Individual differences might be quite important in moderating the strength of dissonance effects. Although cognitive dissonance is a common occurrence in most people’s everyday life, the magnitude of the dissonance they experience may nonetheless differ from one person to another. The purpose of the study in this book is to investigate the relationships between personality traits and cognitive dissonance in a counter-attitudinal advocacy paradigm, with a special focus on the traits of openness to experience and strength of sense of self, and to examine whether the relationships in a novel on-line survey study form were different from the relationships in the standard laboratory setting.