How do we discover a person’s true personality? How does personality appear from the inside (i.e., to the self)? How does that differ from how personality appears from the outside (i.e., to the observer)? Given that people often see themselves differently than they are seen by others, what are the conditions under which each perspective is accurate? These questions are central to understanding who a person really is and, in turn, how much people are aware of their own and others’ personalities. The goal of this dissertation is to examine these questions. I begin by providing a descriptive account of the differences between self- and other-perceptions in terms of positivity and accuracy. Specifically, in the first two studies, I compare how people see themselves to how they are seen by their friends, romantic partners, parents, and siblings (Chapter 2). Then, in the next two studies, I test the accuracy of self- and other-predictions of behavior by comparing them to actual naturalistic behavior recorded from people’s everyday lives (Chapter 3). Finally, in the fourth study, I examine the accuracy of self, friend, and stranger ratings of personality by comparing personality judgments to laboratory-based behavioral tests of personality (Chapter 4). The results show that self-perceptions are more negative than others’ perceptions of them, people are more aware of their own negative traits than their positive traits, and they fail to notice a substantial number of their own characteristics. Observers agree substantially about what a person is like, and their knowledge of a target’s observable personality is quite good. By comparing perceptions of the person from the inside and outside with objective behavioral criteria, we can come to understand the strengths and limitations of each perspective. In fact, the two perspectives often complement each other – one filling in the gaps left by the other. Furthermore, even when both perspectives are accurate, they are often accurate in different ways. Thus, although neither perspective alone can explain the whole puzzle of who a person really is, they both provide different pieces of the puzzle and together deepen our understanding of the person. / text