Self-expansion is theorized to be a fundamental motivation for individuals to add to their abilities, perspectives, and identities. Rapidly self-expanding experiences (like falling in love) satisfy this motivation at a fast rate, and are particularly satisfying. However, novel and challenging activities mirror the experience of the rapid expansion, whether they are actually expanding or not, and thus are theorized to be experienced as if they are self-expanding (and thus rewarding). The influence of such activities on one's self-concept clarity (how clearly and confidently defined one's self-concept is) has not been previously examined, which limits our understanding of how diverse experiences affect clarity of our self-conceptualizations. Further, another common kind of life activity, rediscovery activities (activities once experienced as enjoyable but that have not been carried out for a long time) have also not been examined for their effect on self-concept clarity, nor for their role in the self-expansion process. This dissertation reports two experiments designed to advance our understanding by examining how the self-expansion process influences changes in self-concept clarity through actual engagement in or through writing about experiences of expanding, rediscovery, or control activities. Results indicated that after participating in activities, expansion led to significantly less self-concept clarity. After writing about activities with one's romantic relationship partner, rediscovery led to significantly greater self-concept clarity. An additional outcome included higher inclusion of the other in one's self after writing about a rediscovery experience with one's closest other. These results help clarify the effect of expansion and rediscovery experiences on self-concept clarity and deepen our understanding of the self-expansion process.